Ah, but The Spirit wasn't published as a comic book, it was syndicated to newspapers which, while not exactly a bastion of creators rights, were far more accepting of individual ownership. Even at that early date, a good portion of syndicated strips were owned by their creators, not the publishers. Eisner may have been smarter than some to publish that way, but it was hardly an option open to everyone. Come to think of it, I can't think of a single comic book character that's made it to modern times without corporate ownership.
Keep in mind that even such basic things as royalties and reprint rights weren't introduced into the comics field until the eighties. It does differ from case to case, from contract to contract, but as far as I know, nobody's got movie rights to Batman or Spider-Man stories that they've written for DC or Marvel. If they did, David Michelinie would be a rich man. He introduced many of the elements used in the Iron Man movie, and created the character of Venom that Spider-Man 3 was based around. Again, though, he didn't see a dime.
Absolutely agreed. I'm not arguing that studios are nice people, and they hand out checks to be nice. I'm arguing against your blanket statement that a studio's never handed out a check unless they felt they were legally obligated. Is that the norm? Of course. Is it the case absolutely all the time, with nary an exception? No. Annnnnd, now that we're completely off topic, I'm bowing out.
