1)If you can't understand that the performance of PhysX, like any other game technology, is determined by HARDWARE configuration, then you may as well bow out of this discussion because you're clearly out of your depth.
2) A mid range card likely isn't going to be able to max out PhysX and all the other 3D IQ settings at the same time. I'm sure there are select instances where it can however, because despite what you may think, not all PhysX games are resource hogs. The PhysX effects in Alice the Madness Returns for instance wasn't very demanding.
However, PhysX isn't magic, and like anti aliasing, ambient occlusion, HDR lighting etcetera, it does require computational power. But thats why it has different settings (including an off switch), so that gamers can choose appropriately depending on their hardware.