Just to put an end to the whole "____ copied _____" thing, you can't really judge until you know how the internals work.
The wiimote is NOT copying anything and is not BEING copied by anyone. It makes use of a physical device with accelerometers. It's position is calculated in 3D space by the wiimote, which takes into account the positions of the lights on the sensor bar, then figures out distance, etc from that. It then sends it to the Wii.
The Eyetoy is not tracking humans in anyway. All the eyetoy is doing is looking for some sign of movement using a camera. Where it sees movement, it knows something is happening. You can download programs that do the same kind of thing with a webcam. My laptop came with a few.
Natal is a WHOLE different ballgame. If you decide to ignore the voice activating for a second, just look at all it's sensors it's comprised of! One looks for specific features stored in memory (facial recognition, etc), one detects and tracks movement in a 3d space, and more! Not only does it see something moving, a la Eyetoy, but it tracks HOW it is moving! It can tell if it is moving closer or farther, side to side, rotating on Its side, bendidng forqrd... Everything! It's a very advanced piece of technology.
But on topic, I really think it depends on the support the Natal gets from developers. Being included in a few games definately WONT help it, unless those are AAA titles and are plentiful. I doubt it will surpass the Wii, but it will get mighty close... Look out Nintendo...