who cares? ... just kidding. Mine do the same and I've asked the same question (to myself). I doubt if the heater gives off that much heat. Guess you'll have to put your hand in the water to find out...let us know.
Put my hand on it? Hm... maybe I can pay my sister to that xD I have a fear of water equipement. Especially water heaters, the whole idea of putting part of an electrical cord in water baffles me.
I agree with momar, if it bothered them they wouldn't do it. But, if you are worried they do sell heater guards.