I think it's a major part with the flying limbs & gore as well. For example, if you saw in the Eurogamer Pittsburgh demo when Joel threw that bomb thing with shrapnel in it, it caused both Hunter's limbs to blow off and there was a spray of blood.
Buuuut, in a case with the Violence being turned off, he could have thrown it, but they're bodies would have most likely just flew in one piece rather than the additional realism of having blood and limbs come off.
But what fun is that, right?
What fun is that!? Good sir, I implore you to remove all the gore from Gears of War, and blast someone into a wall. You will literally have nothing but a non-stop laugh fest.