Yeah, but Nvidia dumped all that money into the game. They said they were going to make tweaks for Nvidia cards, and are delaying DX11, by putting it in a patch. I am sure all that money did not buy just a little tessalation support and a free game when you buy an Nvidia card.
Theres no doubt about that dude but that doesn't automatically mean they use physx since the engine isn't built with it. I'm almost positive crytek does not use physx and in fact I'm sure of it since if there was any word of them using physx the amd fanboys would be screaming rivers of blood. Which hasn't happened, thus I can easily conclude they don't use nvidia's physx.