Superman IS a god in most ways. The people of earth can be said to worship him, in awe of his power and character, but he himself will not have any such labels put on him.
Consider, Thor is a god because of where he comes from and because a society worshipped him as such long ago. Thus History records him as a god. If however like Superman he categorically dismisses and objects to such a label as "god"... would he be a 'god'?!
Its a very fine line between Superhuman alien and otherdimensional 'god'. Nobody worships Orion, certainly beyond The Fourth World few in the universe even know of him, so is he really a god...?
Can there be cosmic gods such as Galactus and celestials though, magical ones such as odin and HP Lovecraft elder gods, and gods like darkseid. more of a "physical" nature?