From what Sony told us (I don't have the links to this anymore, so please link if you find them) we know GoW1 hit 3 million, GoW passed 2 million (but no word on 3 million) and while there has never been any announcement, I would be shocked, based on sales, if GoW:CoO had passed 2 million. Thus, sales of the franchise look roughly like this:
GoW1: 3-3.5 million
GoW2: 2-2.5 million
GoW:CoO: 1-1.5 million
So not only is it a franchise that's been selling less every iteration, even at its peak it never even sold half as much as Halo 3 has. God of War is not in the ballpark of the major blockbusters a la Mario Platformers, Smash Brothers, Mario Kart, Halo, and Gran Turismo. The last Mario Party sold nearly as much as all of the God of Wars combined.