Using total trilinear filtering costs about an extra 30% or so performance on ATi cards if I remember correctly even with their agressive adaptive filtering, the number will most probably be similar for nVidia cards.
nVidia are doing some trilinear in UT2003, but not on the whole scene, and nowhere near what they should be for the settings selected in the driver control panel.
As for having a nVidia logo in the game, that should mean the optimisations should be in the game, not via application detection in the driver.
So you're saying that total trilinear filtering will cost an extra 30% in performance in ADDITION to the performance hit already taken by using the bilinear/trilinear combo? Err...
Also, as for the nVidia optimizations, it could very well be in the driver as well as the game... Epic could simply be working with nVidia on optomizing the engine EVEN AFTER the game is shipped and the game can then call for driver optimizations when newer optomizations are created.