The goal of videogames was a lot more concrete back in the PS2 era - graphics and big games. It was really bringing proper-sized video games with no technical limitations to the consoles. But now that the casual market has come in, and games like Wii Sports and Guitar Hero are selling so well, it wouldn't surprise me to see yet another alternative shift in control interface. I'm not sure how long the whole "wave your Wiimote" thing can last, so I doubt Wii will be on the market as long as PS2.
HOWEVER, if Nintendo can ramp up production, I can see Wii selling a whole lot faster still, and so I think it could catch PS2's lifetime sales - definately - but actually in a much, much shorter scale, as opposed to 60-weeks vs. 66 I expect a ratio more along the lines of 2-3:1 time-wise.
