Console multiplayer gaming
I think a lot of it has to do with the advent of decent console multiplayer capability. Coupled with the fact that a high end graphics card alone costs the same as an entire PS3 (and you'll probably spend the same again in 2-3 years when it can suddenly only run Sim Tower), people are taking the logical choice and going console. Especially as most of the big new games are multi platform (COD4).
I for one welcome the change. No more pissing around with graphics/sound/chipset drivers, installing, patches, x-fire, teamspeak, punkbuster, multiple accounts, buying new hardware, patching XP/Vista... then start again when the whole lot needs reinstalling when you get a new board, OS upgrade or a fucking virus.