Both ATi and nVidia have a devrel program, meant to help devs exploit their hardware. The devrel program is not just for companies that enroll in nVidia's or ATi's "Way to Play" ad campaigns. DAoC didn't play badly on ATi cards b/c of nVidia's campaign, but because the developer didn't make the effort to work on ATi cards--the same with NWN. Splinter Cell is a port from Xbox, so you ahve to expect that most of the dev's time was spent on nVidia hardware.
UT2K3 also has that nVidia logo; do you see nVidia cards blowing ATi out of the water? Do you see any glitches on ATi cards? No. Ultimately, it boils down to the developer having enough time and money to optimize for all cards. "Way to Play" is a marketing ploy, and you shouldn't use it as a guide to how a game will play on your card in comparison to an ATi card (though a game branded with nV's "Way to Play" should run well on nVidia cards).