there are a few Physx games out there, and there will be a few more released.. It is just not very common... most physics in games use Havok, or other discrete engines/apps/calcs to achieve the physics in game.
any game that does use the physx engine, can be played with non physx cards, and you will not miss out on any game play, but you will miss out on some extra fog, or flag whipping. lol Mirrors edge is a great example, with/without Physx effects is pretty cool, and when you shoot a flag, it will re-act differently than without physx..
Nvidia has been making it nearly impossible to use hybrid setups, allowing it, not allowing it. so I don't think Digital Storm will be doing any of them? but maybe if you call them? lol