I have to disagree on this one. Everyone I know with a Xbox 360 has them in their livingroom, hooked up to a big-ass HDTV.
Ofcourse you can attribute that to my age, and the fact that I don't know too many teenagers, but for the teens in my family, if they are gamers at all, what they have is a PC in their bedroom. Console-gaming is if not exclusively at least largely a social thing, and thus makes more sense to have in a room made for socializing.
While my argument isn't backed by solid data and mostly relies on my own experiences, you can't really claim yours is any better either.
As for as the Xbox 360 goes right now it is a massive success. It is one of the top three consoles in a market where there used to only be two. That's big achievement in itself.