No, I'm not saying nVidia does a' magic trick' to get 2 viewpoints from one image. As far as I can gather, you're the one saying that
But to reiterate what I said two posts up - It doesn't get two viewpoints from one image - because that clearly wouldn't work.What the 3D driver does is calculate the whole scene from two viewpoints. You can adjust how far apart those viewpoints to increase the Stereoscopic separation to your tastes, but the whole thing still relies on two discrete viewpoints of the scene being combined to make one Anaglyph. Or other graphical representations suited to other 3D viewers.
If it just calculated one viewpoint, you'd end up with a flat image - you need two viewpoints to get any kind of perspective, so that is what the driver does. This would be the equivalent of your 'Two Cameras'. This is very much how our eyes work. And how the driver works.
Consider that anything you see on a monitor is just a graphical representation of a virtual scene calculated by the PC. All the 3D driver really does is provide a graphical representation of a virtual scene from two different angles at the same time, in real time.
As an aside, it plays the whole game in 3D - you can wander about the lot if you like, and that would all be represented in real -time anaglyphic 3D, perspective and all.