Why does pizza taste better reheated?

Pizza is nice when it's fresh, but for some reason it's even better the next day after you heat it up.  (Not bad cold, eihter).

Why?

Reheated Italian, American, or any other kind of pizza on a broiler, in a brick oven, in a conventional oven, in a microwave, on a grill, or in a microwave is nothing like the original.  If someone could invent a way to keep the original flavor in a reheated pizza, it would be the best invention since ---well, since the pizza!