You are right, according to Chinese medicine you should keep it warm. But what is happening is an inflamation reaction (right?), this can be good because it can stimulate healing, but it is also bad because it can cause damage. Icing an injury will make the pain less and I think that's why it is done. It also reduces bleeding because the bloodvessels will narrow.
I'm not a doctor or anything, so maybe the thing to do is ice when the injury happens and warm when the situation has stabilized. But don't take my word :P