I think you misunderstand what PhysX is about. It is a physics solution (library) for games. There are many physics solutions available, and you can also write your own.
So yeah, true, you didn't fall through the floor in other games, but those games also had a physics solution, even if those were not called PhysX.
In the past, physics solutions for games may have been fairly simple, but now that we are working in big 3D worlds, physics can become quite complex. That is why a lot of developers choose middleware such as PhysX or Havoc. But that doesn't mean that you can expect everything to react "realistically". It doesn't come out of the box that way. And we did play around with realistic-physics-based gameplay and objects, but finally decided not to go all the way, because the effort just wasn't worth the extra value the player would get from it.
I mean, to make everything in the world behave realistically would give the minimum specs yet another boost, and we would have needed some extra programmers. And we would have to give artists and designers a lot of constraints as to how they should build and decorate their levels, and how to write quests. All this work for the same old "you can kick a heap of logs down the mountain" trick seemed pointless. At that level, it's just a gimmick, and doesn't really make your game richer.
I'm not saying we'll never do that. But if we were to fully integrate realistic physics, we would only do it if it really makes a difference, and if we had lots of fun ideas for it.
PS: You don't _need_ an nVidia card to make it work. But if you do have an nVidia card, the graphics card will take over a lot of tasks that are normally given to the processor.
PPS: I cannot help myself. I'll keep on posting here, even though I know I don't write German. I wish I could write German. I can read German, so don't answer in English if you don't want to. And if you don't want to read English, skip my posts
And no, it's not really my job to write stuff here, I'm doing this out of my own free will