nVidia started it and XGI is continuing the trend.
I think u forget the quake / quack issue... or did nVidia cheat before that happend ?
anyways, application specific optimisations were used all the time for the 3DFX cards, and why shouldnt they, if they enhance performance, and adapt the way the GPU handles that specific engine, but a cheat is an optimisation that only superficially optimises it (if it were to optemise it so that a standard Q3 timedemo looked normally but everything out sight was clipped, that would be a cheat imho. but if it's overall improvement then you cant argue that app specific optimisations R bad.