Why it won't happen:
1. Casual gamers don't buy 2 consoles. They already have a Wii.
2. The economy is shot to hell for at least another 3-4 years. Refer to reason #1.
3. Wii motion controls have not been negated. With Motion Plus, the Wii now has controls that are equally functional as the Move setup, how they are tracked is simply different, but both are similar in accuracy.
4. Sony isn't dumb enough to stick with the PS3 past a maximum of 2013, despite what they say. When Nintendo and MS put out new systems that are superior to the PS3, people will stop buying PS3 units. Sony knows this, and will have a PS4 out by 2013 at latest.
5. Nintendo still has the ability to do another price cut, plus Zelda is coming out in the spring, which is one of Nintendo's biggest system movers. With the holiday coming up, Nintendo will likely outsell the PS3 again by default, and continue this trend next year due to the new Zelda game coming out.
Sony's pride is what was their fall. If they laucned the PS3 at $350, it would have sold like wildfire. Asking $600 was shameful and they got what they deserved for their greedy move.