IMO, MP wouldn't work well with this kind of game. As one guy said, he wanted to have gangs against each other and so forth, while they would be super fun, I think that would turn into one ugly deathmatch pretty quick. Pretty lame, if you ask me, when there's so much more to do in the game. This game works well as a SP game, granted some form of MP ALWAYS makes a game last much much longer nowadays.
I dunno, I just can't see a bunch of 14 year old kids who buy this game wanting to adhere to an actual gang/clan(like in any online RPG) and methodically kill the other gang. It'd be more like they hop in a car, drive around like idiots and run over whoever they see, with no care for what the rest of their team is doing. And deathmatch would just be boring, cause who actually plays DM games now? Team-based/co-op is the only way to play if you've got halfway competant teammates.
I'm not angry that they're not including it, I'll probably still buy it just to see what the new 3D version is like.