This means this game is only tested and tuned for Nvidia. There are a lot of PhysX games, PhysX has a CPU fallback mode, this is why all of them also work with ATI and Intel grafic hardware. I also ran it on Intel already. It would also be illogical if a well-established game engine like the Unreal Engine only works on Nvidia cards, no game developer would use it then. Just try it, it is really well made :)