The Wii will surpase the 360 in total sales by the end of the year, so holiday sales is pointless. Even if the 360 were able to outsell the Wii for 1 month, it has had a year head start and is already getting it's butt handed to it. Price drops anyone?
If Wii Fit came out in November, then it would be all she wrote for the other consoles. So, it is probably better that it is coming out in January so they can up the supply (as much as possible) before even more non-traditional gamers start buying Wii's.
Halo 3 won't get more hard core gamers to 360, they already have their 360.