Oy...
So terribly false. I have a 2008 iMac that plays *most* games wonderfully, at native res of 1680x1050. Starcraft 2 Beta, Half Life Episode 2, Bioshock, etc. etc. I'm no "n00b" when it comes to gaming and performance, either, I've built numerous high end machines and I am extremely picky... I won't play a game if it's consistently falling below 60fps.
A little bit of tweaking settings and managing your computer well is all it takes. I keep a clean boot camp partition with XP Pro and no junk programs.