The Good Ole Sweatball

Here is something to think about...

A pitcher is not allowed to spit on the ball for obvious reasons, but how many times have you seen a pitcher get a new ball from the ump, take his glove off, get all the sweat off his forearms, and rub down the ball?  I understand pitchers wanting to rub down the ball, but how are they allowed to take the sweat off their arms and rub that onto the ball?  You're not allowed to spit on the ball so to me, you shouldn't be allowed to put your sweat on the ball either.

If anyone has some input to this, feel free to comment; I'd love to hear your thoughts!  My only guess is that the umps believe that the sweat will evaporate before the pitcher throws that next pitch sorta to the affect a pitcher can lick his fingers as long as he doesn't go straight to the ball afterwards.