I think what's happening there and also with Gamestop's PS3 situation is that Nintendo and Sony are shifting units around between retailers. I suspect there will still be 400,000 PS3s and 1 million Wiis, but bigger retailers are getting a bigger piece of the pie by cutting deals with Sony or Nintendo.
Think about this: You're Wal-Mart, and you can make $7 per Wii. You know every single one is going to sell on launch day, so if you get 50,000 Wiis, you make $350,000 right at opening. If you give Nintendo a bunch of free advertising, maybe Nintendo gives you 100,000 Wiis, and you're making $700,000 right at opening. Not only that, the more units you get, the more games and accessories you sell too! So actually your profit may go from $500,000 to $1,000,000. There's absolutely no question if you're going to sell that stock, it'll never be marked down...it'll be sold within the day. So Nintendo/Sony thinks this is a good deal, and the smaller retailers get the axe.