I think because the Gor novels were first accepted as mainstream SF, and the Ginger movies as standard sexploitation detective movies, they gave viewers and readers who would never ordinarily touch an overtly kinky title a certain license to read a Gor novel/watch a Ginger movie. Kind of the way a lot of guys who'd never be seen buying a copy of Maxim or FHM will buy a copy of the Sport Illustrated swimsuit edition because it's not not a men's magazine, it's Sports illustrated.
(I've got something more along these lines coming up, just can't decide if it's for the website or the blog.)
But things were different back then: the common perception was that bondage was something only practiced by beret-wearing beatniks in New York City with the aid of capri-pants wearing hotties like Bettie Page. It wasn't something that people expected to see in mainstream books and movies, unless presented specificaly as a bondage story, like "Story of O." So when they watched Ginger or read the Gor novels, they didn't really see it.
Of course, people are a lot more sophisticated about bondage nowadays, but they're also a lot less sensitized to it in certain respect. That is, during the recent episode of "Desire" where the bad guy spent so much time fondling and gloating over his bound victim, there's a DEFINITE sexual bondage subtext going on there. I think modern audiences would tend to note and not be particularly upset about this because it's just something a director might do in an edgy damsel in distress scene. Their awareness of sexual bondage has in a sense desensitized them.
So, the quest is, could someone do a bondage series of some kind now in a mainstream venue, without having it immediately recognized for what it is? Would the increased awareness of sexual bondage make them more apt to catch on, or would the desensitizing of audiences to sexual bondage imagery make them less apt to catch on?
And for bonus points, what sort of venue might work? That is, what sort of mainstream movie/TV/novel genre might work as effectively for bondage imagery as John Norman's sword and sand fantasies, or the Ginger movies' detective genre?