One thing that could go against New Super Mario Bros. Wii:
Mario Kart Wii's sales are nearly directly linked to the Wii. It's a game you pick up together with the Wii. It seems that ~ 25% of new owners pick up Mario Kart Wii, actually.
Now, Mario Kart Wii seems as if it will hold up ~20% after christmas as well. You will also have Wii Sports Resort, which looks to sell to a good 30% of new purchasers. You also have Wii Fit and Wii Fit +
As a result of this, New Super Mario Bros Wii is launching on a far larger competition than Mario Kart Wii did. It launched in competition with Wii Fit and Mario & Sonic/Brawl, but that's still less than what NSMB Wii is facing.
Due to the evergreen nature of the Wii games, NSMB Wii is launching against Mario Kart Wii, Wii Fit +, Wii Sports Resort and Mario & Sonic 2.
I don't think that NSMB Wii will have less ability to rely on legs than the previous evergreen titles had. It will have to depend on people who already own a Wii buying it too. As a result, New Super Mario Bros Wii should be rather front-loaded, and then it may fall down to Mario Kart Wii esque numbers after christmas, or quarter 1.
I'm sort of suggesting that the later a Nintendo game comes out on Wii, the less it will sell.
