Seeing as I actually watch the news pretty regularly, and bother to read up on things like foreign legal systems, some clarifications, for both sides of the pond.
First, the generalities. The main difference between the typical European style systems and the US is indeed presumption of innocence. In the US, you can only be incarcerated without bail because you are considered a flight risk or a danger, preponderance of evidence, previous actions and means are taken into account. The standard for arrest is also quite a bit higher than in most countries. Most of the time, people are out on bail awaiting trial. The only time they are guaranteed to be locked up is between their initial arrest, and their first bail hearing. On the other hand, quite a few European countries do not go for circumstantial evidence, we in the US have a few people on death row from evidence you couldn't get a trial with in most of Europe.
The typical European system can however incarcerate more easily, often with far lower requirements than we have here for an arraignment. You then get to stay there, with evidence standards coming into play in order to keep you there. Bail for a murderer is not a common thing, as it is here. Guilt is also typically not beyond a reasonable doubt, the "standard" in the US. I put it in quotes because we lie our asses off when we lock someone up on purely circumstantial evidence as was the case with Scott Peterson, a guy on death row. 
I'm not saying one is better than the other. Ours would be, were it still pure, but the lawyers run it these days so it's a disaster instead. Between the evidenciary rules that get people off just because someone didn't dot their I's and all the bullshit they do to hang someone when the media jumps on them, we've got a real cluster fuck going on...
For Amanda Knox in particular. There was no media support in the US, sorry guys. Pressure from the US getting her out of a murder rap is just not how it went down. The chick was pretty much railroaded over here too, they were doing that foxy knoxy crap 24/7, and had her black listed as some kind of sex crazed drug fiend of a devil worshiper. The cops did the typical cop thing(sorry cops, but you know your type tends to have power trips and run off assumptions till hell freezes over:)), and the prosecutor was crooked enough to try and make it stick and bury evidence that proved his theories wrong. They convicted her the first time around knowing the main perp lied his ass off about them being there, and that they couldn't have done it. Our moron media over here was no less idiotic than the local media was, and bought his bullshit, hook line and sinker.
