The Wii will NEVER drop below the XBox 360 or PS3 in total sales, for a few key reasons:
1. Microsoft couldn't sell rice or raw fish in Japan. The Japanese people have loyalites to Sony & Nintendo, and for the most part, won't buy a Microsoft console.
2. Sony's PS3 is over-priced. Well, maybe it's a good deal for the hardware that's inside the console, but most consumers aren't willing to pay that much for a video game console...especially when they have cheaper alternatives.
3. The main reason the Wii will win this generations' console wars is because Nintendo has practically cornered (and created) the casual gamer market. Basically the hard-core gamer consists of all those that played video games in the pre-Wii era. The casual gamers are all those that DID NOT play video games. Obviously, there are a lot more casual gamers than hard-core gamers...and Nintendo knows they can make a boat load of money off the casual gamers. Just wait until Wii Fit comes out. Every overweight American will want to own a Wii.
I'm old school and consider myself to be a hard-core gamer, but I must admit that I love Wii Sports. For replayability, it's got to be up there with some of the greatest games ever like Ms. Pac Man...and it's a great multi-player game.

I'm happy for Nintendo's recent success, and I can't wait to play with some of their new innovations in the future.