Yeah, the driver thing is the only reason I can think of. ATi until the 9700 had craptastic drivers, and I still don't completly trust that they're okay (though if I was buying a video card right now I'd get the Radeon 9800 Pro in a second, considering for $300 you get a card that's a gazillion times more powerful than a $500 Nvidia card).
And what's this about Nvidia being faster "on today's games"? ATi is faster on today's games, and with the games of the very, very near future the performance and image quality difference is just astronomical (what with a $150 ATi card outperforming a $500 Nvidia card on games coming in the near future).