The Wii's will move alot more consoles at first, maybe not overall but certaintly at first. They appeal to the casual gamer, the person who has 30 mins here or an hour there to blow and not the guy who races home from work/school and hops on the ole gameing machine. Its alot more affordable, many more children in the 10-16 range will have them because their parrents are more likely to shell out $249 instead of $299 or $499. The price doesnt really undercut the 360 THAT much, but the console in itself is geared more twoards younger kids, middle aged adults and the casual gamer in general.
I was quite shocked that in the area im in ALL the PS3 pre orders flew out of the stores so fast, didnt think that many people were willing to plop down that kind of dough.