PC gamers market has been moving away to "casual" space since the rise of World of Warcraft. After I start playing WoW my PC gaming spending was reduce pretty much to $15.00 a month for WoW subscription. I used to buy new game monthly (like I do with Xbox 360 now) but with WoW you don't really need to. Everytimes you fired up your PC you automatically just log into WoW.
I only know one person that still gaming heavily on his PC (he doesn't play WoW) , majority just play browser games or Pop Cap games.
I am sad looking through my old boxes of PC games, there are so many good games by MS studio - Mechs Warrior , Rise of Nation, Ages series. Getting out of PC space is nothing new however.