Hmm Goa, this post brought up an interesting idea though I'm sure there's going to be ways to shoot this down. What if, as far as all the complaining is concerned, they released Rebellion as a stand alone version of the Sins saga and incorporated -64bit into it? (typing this I already see there would be financial losses from this choice, problems with distribution costs/methods, consumer's preference and or system limitations, and much more work involved on the project they probably couldn't afford at the time)
Anyway, buying just the expansion after getting Trinity shouldn't be all that pricey anyway, especially off of impulse. Wasn't trinity cheaper off impulse than other stores during it's release? and on top of that they have it on sale so you could cover Rebellion's costs with whatever you save from Trinity(ah, that might have been one of their financial rep's ideas, good call, selling the older required product to run the newer is an old method but it works 90% of the time[for anyone but EA anyway, they use the foot-in-the-door technique too often, kinda exhausting just to look at their products now])
Hurray I'm on a roll with these text walls, I should probably sum things up better.
But Goa's right, they very well may not release any hard copies except in a few places so downloading from impulse may become a requirement once it's released so get that bandwidth updated you 56k out there, you know who you are ;O