You know, as much as I find real genocide to be terrifyingly evil, I really can't see the races in Sins settling for anything less than the complete annihilation of their enemies. Consider the backstory and races' points of view.
TEC: Half the planets on any given map used to be TEC. Now they're populated by ailen scum who enslave us to build their ships and suck our worlds dry of resources to rebuild and refuel their fleets, all the while fully intending to leave us behind to deal with whatever evil thing it is that they're running from on our own. As for the Advent, it helps if you look at them like the Borg or their analogues in other sci-fi settings. They're relentless in absorbing people into their bizzare culture of genetic manipulation and psychic mind-control, and anyone who doesn't give in is killed. Furthermore, the TEC has been at war for 10 years prior to game start. They're tired, they're bloodied, and they cannot afford to toss away the lives of millions of soldiers making ground assaults on every planet they want to (re)take. At the same time, their survival demands that they do retake as many planets as possible, and deny as many planets to their enemies as they can.
Vasari: Their backstory seems to indicate that they weren't very nice people to begin with. Couple that with the fact that they're on the run from some unspeakable evil, time is short, and they need the resources to repair and refuel their fleets more than they need the human laborers they were going to leave behind anyway, and they've got no reason to care. On top of that, they've got precious few foot soldiers left and can by no means afford to put them to waste assaulting even one planet. Did I mention that they really don't have the time to wait for a planetary invasion to succeed, since the great mysterious terror is chasing after them?
Advent: The Advent left everything behind to return to their home world and get revenge on those who exiled them. If they fail, they're wiped out. On top of that, they've got a thousand years of ritualized hatred for the TEC, who treated them as less than human and kicked them off their home world. Anyone who does not join them is in the way. So it makes perfect sense that, in their holy war, the Advent would have no problem with wiping out every single person who did not surrender to their collective will. As for the Vasari, I'm sure they're just as willing to enslave and exploit the Advent as they are the TEC, and the Advent can't be happy about this. The Advent are not about to return to their homeworld just to be enslaved on it by filthy aliens.
So, as I see it, it doesn't make much sense for any of the 3 races in Sins to even bother with fighting their enemy honorably. In MOO and many other 4x games, the backstory doesn't usually pit all the races in a free-for-all war for survival from the very start, or give them every reason to hate each other with a burning passion unrivalled by the sun. Again, I'm not approving of genocide, but I find that in the epic story of Sins it just makes more sense than planetary invasions. The TEC doesn't have the resources of w40k's Imperium of Man, that they could throw away millions or billions of lives on any given planet, and none of the other races do, either. To me, the planetary bombardment mechanic just reminds me of how terrifyingly desperate the 3 factions are.

Consider the very name of the game. I don't want to go into doctrinal debat, but I think it would be safe to say that genocide is considered a "sin" against the race of your choice. Many of you thought of the "pink pony" on your opponents world, but what about the "pink pony" on your worlds? What are you willing to do in order protect the "pink ponies" on your own worlds? What "sins" are you willing to commit to bring safety to the TEC, vengence and justice to Advent, or survival to Vasari?

Of course it is just a game, but it is a good thing to see that our gaming community as a whole has some deep thoughts!   

More than happy to show them some of the finer points of my culture, such as the slave pens, the harems full of their women, and the cafeteria which serves their young as a delicacy.

Nutritious gruel three times a day is better than some fatty, greasy hamburger right? And just imagine the muscle tone they'll achieve with all that manual labor building me another vacation palace!

Sure it takes a show of force to get most folks to see things my way, but I can assure you the citizens under my rule are much happier and more productive for it.

So yeah, bombing works great for me!

Wait wait wait. I don't think we're all on the same page here. You aren't wiping out the whole population.

Virtually all the people in this game are TEC humans, but simply aren't included in any stats anywhere. Read the planetary population research, especially for Vasari (who develop better ways to oppress and control more native population). Sure, they drop some number of their own to control the planet, but the bulk of the population are occupied people. Similarly, the Advent are "spreading the word", not merely with culture, but directly with planet upgrades. There is already a population there, and there always is. And then the TEC stuff doesn't need to worry about oppression or conversion, because those people are TEC citizens anyway.

The beta descriptions hold true: the infrastructure etc. that you bomb is the government / military infrastructure. Note that you can happily reduce the population to zero without taking the planet - and it just starts going up again when you stop bombing. The "population" are those working directly for you. There is a - presumably vast - population on every plaent which isn't modelled.

Sure it's not a perfect description (some of the techs' description contradict it all, particularly the ice / molten colony research), and it'd be nice if the game explained this a little better, but I am one of those who thinks glazing planets is a stupid game mechanic. I'm very glad Sins doesn't have it - or at least, it doesn't quite, if you look at it carefully.

Yep, I see the obligatory "pussies" finally made it into the comments. lol. I'll agree that there are many different playing styles, and that some may not have a problem with mass killing on a planetary scale. How about looking at it from purely economic logic - why waste an entire planet's infrastructure and workforce if you can bend it to your own needs with an occupation?

A second option is always a good thing to have, whether your are a tyrant or just an enlightened despot.

A planet's population dying off completely during a siege is retarded. Yes, some should die, but not all. If siege weapons were powerful enough to kill hundreds of millions (or even billions) of people, they'd also have the negative side-effect of destroying the planet to a degree where it'd be uninhabitable for hundreds, if not thousands of years.

Am I on ignore? You don't kill the whole population, just the folk working directly for the controlling empire, and they're probably just buggering off (note that pop goes to zero very quickly, with infrastructure taking ages - and the population comes back quite quickly from zero when the bombing stops).

You capture a planet with a "native" population that simply isn't shown since they're presumably unarmed and irrelevant - read the Vasari civ techs. Their upgrades let them oppress a larger number of the planet's population. Effectively, each side takes the planet and sets up cities etc. for people to work directly for them. Which makes sense since most of the resoures are in space.

It's not totally clear cut, but I think it's fairly well implied and gells with what they were saying in beta.

Are you seriously pulling out practicality of 'intergolatic war'? There is no such thing

I would enjoy having a 'takeover' option as demolishing the planet seems like a backward attempt at colonization. Culture works, but how long can you realistically wait to advance 1 planet? Get a multi-star system going (as said before) and you might as well read a book. Perhaps more depth or balance to culture takeovers?

I like ur thinking....

Humor: See, this planetary bombardment genocide thing is inconsistent with the back story!

When the TEC first realized way back there that the Advent had to be ejected from human space, they should have just committed genocide, bombarded the planet, end of problem. Then there would have been no pesky Advent to return and make nuisances of themselves. But no, they had a bunch of bleeding-heart liberals in charge who was afraid to push the button!

Serious: Seriously, though, I suppose I am a bleeding heart liberal myself because I really do find the planetary bombardment disturbing. Sure, they are doing it to shorten the war. But it sends cold chills down my spine. It makes me think of Hiroshima and Nagasaki. Hey! Now there's a thought! How about a selection of short cut scenes after bombarding a planet that would be genuine clips from those old black and white films the Japanese government made of the aftermath of Hiroshima and Nagasaki? heh heh heh Those horrors would get this game some media attention, eh?

Well, seeing as this IS a game, I don't see how bombing a planet should matter in the slightest, why did you buy Sins in the first place? And if you find planetary bombardment of fictional people on a planet which is made up of pixels disturbing, then you must have NEVER bought any form of video game that included violence in it whatsoever, (FPS's, RTS's, RT4X's, the works) so whyd you even buy sins if that is the case? I mean, its a game about intergalactic domination, kill everyone else, be superior, that much was made clear right off the bat, heck, the games name is SINS of a Solar Empire. If thats not a clue, I don't know what is.

Ow come on people lol its not like theres any gore, I dont want to feel like Im playing "Rainbow" the game in 6 months lol

and Im not talking rainbow 6 either hehe, more gore I say muhaha

The edit button functionality is wacky on this forum , in my below post I meant to say "dumbed down"

As for population degradation to the point of zero I imagine many forms of futuristic bombs would have that effect.