Opinion (that seems to be the popular one I'm rooting for): After the first exchange of blows, from that point on the fight can be judged to award points to the winner. If someone's gone past the time limit then you can get a free hit on them, so even if they were winning up until that point that would likely change, so it's very unlikely the person who left could still be declared the winner unless we take away the auto hit rule. 

Forfeiting gracefully shouldn't allow you to keep points any more than a normal defeat (although either way, at the moment, we don't lose points), it just saves a bit of time. Otherwise you could forfeit right before defeat and save point loss.