Forget bringing up Mario Galaxy, nobody believes it will sell that poorly.
This is what we're looking at:
http://vgchartz.com/swlaunch.php?reg1=All&game1=®2=All&game2=®3=America&game3=Call+of+Duty+4:+Modern+Warfare+-+X360&weeks=11
I imagine Modern Warfare 2 will sell more or less like this, except with a much bigger launch week. I'll just throw 2.5mil onto MW1's total and say it'll end at 5.5mil.
Let's look at another game, Mario Kart Wii (which I am assuming to have a similar sales pattern):
First 11 weeks: 2.5mil
11 holiday weeks (starting week ending Nov22): 2,507,944
133,068 + 263,749 + 1,326,343 (Dec) + 311,372 (Jan) = 2,034,532
MKWii's America total, by which I mean taking the sum of its launch period and its holiday period, still only sums up to ~4.5m. That's probably the absolute best case scenario for NSMB Wii, so the bet isn't happening. To make things slightly worse, Modern Warfare 2 has 5 extra days on NSMB Wii's sales, due to releasing earlier.
I'll predict 4mil for January NPD. It's probably on the high end, but I have faith in 2D Mario. Worldwide, I expect NSMB Wii to overtake PS3 MW2 sales by the end of 09, 360 MW2 sales by April 2010, 360 MW2 US sales (Reggie's bet) by Oct 2010, HD total sales Q3 2011, and total (PC included) by the end of 2011.
If this ends up totally off, it's because I'm hyped for the game (and am now expecting MKWii-like sales), so please put the blame on any of those fools rocking the damn Koopa Kids' avatars.