Not only not unique, but redundant and no developer in their right mind would choose CUDA (or the AMD equivalent that never took off) over a standardized system and alienate over half of their potential audience.
Well it's all good news to me because had CUDA dominated I might have speced my next build with a 16x, 8x, 8x MB to use dual two slot GPU SLI with a single slot midrange GPU for PhysX. Knowing this I can go back to the more affordable and simpler dual vs tri SLI MBs and probably have less driver problems because of it.
I have read benchmarks indicating two GTX 280s and one 9600GT for PhysX beats 3 GTX 280s, but that would only be in the few games that support PhysX. If DX11 is as good as they say it is, two top shelf single GPU DX11 cards may beat 3 top shelf single GPU DX10 cards. However if that's the case they'll also price them accordingly.
Back OT though, DiRT 2 looks so good it may be the game that makes me finally break down and get a wheel/pedal set. Still dreaming of an economy version of the G25 with no clutch and H shifter. I've seen the Driving Force GT at pretty low prices, but it has cheap pedals.