PS2 = 120 million userbase, GoW sold 3,2 million at it's best.
GC = 21 million (I think?) userbase, AC sold 3 million at it's best.
On handhelds:
AC: WW = 9,5 million
GoW: CoO = 0,75 million
Wii = 27,7 million userbase (at the moment).
PS3 = 13,6 million userbase (at the moment).
Let's check this, as well. GoW2 lost by 1,1 million to GoW. AC: WW won by 6,5 million against AC.
Do the math. While DS isn't the same console as Wii, it's pretty likely that many who own a DS will own a Wii. It's also pretty obvious that anyone who has the game on DS and owns a Wii will buy it, because of it's great reception.
To further continue the discussion, let's consider the fact that GoW is a fairly new franchise entering into a pretty old genre. It has to match up against all other games of it's kind, who are also moving upwards on the market.
AC, however, is (as far as I know) pretty unique, and it's own kind of game. So if someone wants an AC-type game, they'll buy AC. If someone wants a GoW-type game, they've got lots of other choices to consider as well.
Also, let me reassure you all that I am not biased. I dislike both AC and GoW.
