You guys betting against the Wii are assuming Nintendo doesn't increase production, at all, this year.
Considering it's still selling out and they also want to launch in China/India, they will have little choice but to increase production. That alone basically guarantees them 50% by end of year.
Wii Fit will also increase demand more than it is now. I fully expect it's marketshare to be somewhere between 50-55% by end of year.