Your whole post reeks of bizarreness to me. D&D was popular with teens, but when was it ever marketted as a game for teens? None of the fiction is YA fiction, except for one or two unusual Dragonlance series that I only recently discovered at the library while looking for a book for my son to read. It's all modern, "adult" fantasy. All of it. And Saturday morning cartoons were for teens? No, they were clearly for much younger kids than that.
And that idea that without drugs and sex, a product doesn't appeal to adults is probably the most bizarre implication of your post. Seriously, Whiskey Tango Foxtrot.
Well, I'd say it was marketed for teens when the ads are on the back of comic books. Is that marketing to adults? You even admit that cartoons are not marketing to adults. So, which part are you not understanding?
Umm, as far as the novels go, I go to the local library and they're all sitting right there in the young adult section. Same as they were twenty years ago when I went to other libraries as well.
So, ok, let me reverse the question. What about D&D is directed at adults? I mean, if the themes are all PG-13 or younger, there is little or no content which is not readily available in the same, so, what about the game is being directed at adults?
Heck, even look at most hobby stores. You've got D&D sitting beside CCG's and comic books. I'll buy that comic books might be an older hobby now, considering the price, but CCG's?
See, I look at something like White Wolf and think, yeah, that's directed at an older audience. You have some mature themes there that probably aren't all that much of a good idea for a 13 year old to be exploring.
But, I cannot think of a single thing about D&D that would even remotely give me pause handing to someone that age.