Like its been mentioned Physx 2.x.x is crap, 3.xx ain't that better either. Actually physx 3.x.x its what physx should have been from the start, but Nvidia has to milk it so they can sell more gpus..
Physx 2.x.x SDK code is inefficient single threaded most of the time, so they make you believe you actually need a separate gpu for it


Also there is a rumor Nv might be giving out cuda language, so if this really happens we could see amd gpus running physx via cuda -openCL ? language, but then again openCL Bullet is much better.