It seems nVidia is just looking for something. They say the drivers disable optimizations on windows smaller than 500 pixels on a side, which is probably why AMD did it, when was the last time someone played a game that was smaller than 500 pixels on one side? If you did, does your card really need to do optimizations on that game when you are not going to be noticing it? No, it doesn't.
I would consider it a cheat if it was a game, played in full screen, at the highest allowable resolution for the monitor, and the card disabled optimizations.