The Xbox 360 does have a ~50% userbase size advantage in the western world over the PS3. Add to that the fact that Halo is probably the 1st/2nd biggest name in console FPS games (depends who you ask and it can go either way depending on the day), reasonable sales of some RTS games in the past which should lead to some decent if not great sales.
Killzone 2 is dark, lacking in local play and the controls may be subjective to a lot of less experienced gamers and even many experienced gamers. It doesn't seem that they designed the game to be liked by the widest of demographics. People who need glasses hate dark games in my experience, people do talk and share their experiences with games and Co-Op is an important part of this, and games must be accessible otherwise the other good in the game will go completely unappreciated.
I say its definately possible!
Tease.
