All this is true, but it's also true that there's something of a historical rivalry between Marvel and DC, or between their fans. Although, as I said, that hasn't stopped countless people from working for both.
Yeah, I've always thought the "rivalry" was silly. It's not like they're sports teams or whatever. Ditto for Star Trek vs. Star Wars.
(Says the guy who has written at least eight books for Marvel and six for DC!)