IGN had an interview about the upcoming Call of Duty 4 game:
IGN AU: Obviously they exaggerate a lot of things to make it a better game experience though?
LTC retired Hank Keirsey: I would say it's much closer to reality than one would think. The sound of the weapons firing, the way the weapon sight looks when it comes up, the movement of the soldiers, it's all done very well. As an old soldier, when you look at a war movie you don't look at the good things you see. You look at the bad - they're all bunched up, nobody would wear a chin strap like that, he's got the wrong patch on, he's wearing his rank wrong, his medals are out of order, that asshole didn't know what he was doing. You see every error.
So when I look at the game, and I see that the Javelin missile is flying too high, that's an error. But they know it's too high, but it's a compromise. Same with the smoke grenade - a real one takes fifteen seconds for the screen to develop, but that's too long for a gamer, their attention span is too short, they had to speed that up.