It is quite possible that GOW3 could sell 4-5 million lifetime, but I am not sure it will hit the 4 million mark in 2010-- it all depends on how accurate the vgchartz numbers are.
I personally think the GOW3 sales may drop off a bit after this month once most of the core audience has already purchased a copy. Most of the PS3 ownders I know have opted to rent GOW3 rather than purchasing it. The main reason is that we feel GOW3 is a must play game, but that it is pretty short and has very limited replay value.
I rented it last week and thought the game was superb, but I am glad I only payed $8 for the rental rather than $60 for the full game.
It will be interesting to see what the attach rate of GOW3 is with new PS3 owners. Since Sony are selling over 200,000 PS3 consoles a week, GOW3 maybe able to generate quite a new audience. There aren't nearly as many exclusives on the PS3 as there were on the PS2, so I think GOW definitely stands out more in this generation than the past one. I definitely think that GOW3 is one of the 5 must-play titles for the PS3 along with Little Big Planet, Metal Gear, and Uncharted 1 and 2.
Most anticipated games of 2011:
Uncharted 3,Legend of Zelda: Skyward Sword, Rocksmith
Modern Warfare 3, Super Mario 3D