We have in this discussion a bit of a mix between seeing "growing up" as meaning becoming critically acceptable, and becoming mass market acceptable.
I don't think the two are mutually exclusive. I also don't think you need overwhelming success at either for RPGs to "grow up".
Agreed.
Critical acclaim? A well written setting can be as compelling as any short story or novel, and it is conceivable that it may even inspire the creation of such.
Mass market acceptibility? Well, start by NOT releasing bad derivative works- D&D movie #1, anyone? If you release good genre fiction, it can stand on its own. I think this Summer's list of blockbusters is an indication of this- almost every one was a derivative work of genre fiction.
In general, that's the starting point for acceptability.
In the USA, though, there is an additional set of hurdles not really faced in most other countries- the power of our religious right coupled with the history of the "Satanic Panic" of the late 1980s really stigmatized the game here. Some people simply don't realize that D&D is just a game, not a gateway to eternal damnation.
Maybe Comics and SciFi didn't actually do anything to "grow up", maybe they just caught the wave of cultural zeitgeist at the time. Maybe D&D and RPGs just missed their wave, maybe Gen X'ers just don't have the oomph to power their niche stuff through (I realize not all gamers are Gen X'ers, but that is when D&D came on the stage). Comics and SciFi rode the Boomers into the mainstream, but D&D/RPGs got overrun by technology before it had a chance to "grow up"...
Actually, both did change their character to become more mature.
In sci fi, you saw the rise of anti-heroes, and characters that no longer acted like their pulp fiction antecedents, but like you and me. Instead of a futuristic take on manifest destiny, more stories concentrated on logical consequences of RW actions...translated in time and space in order to be more palatable.
In comics, you saw that in several ways- graphic novels taking on RW subjects, like in
Maus, or thoroughly fictitious characters with RW problems, like Tony Stark's alcoholism, Northstar's homosexuality, and characters actually dying.
In D&D's case...well, role-play in general, you need products that have mature and tasteful art (something not every company has gotten the message on yet), good writing, quality binding and printing. Some products have achieved all of this, but they're still the exception rather than the rule.
The Gen X thing has some merit. We simply never had the purchasing power of the Boomers, and we've already been surpassed by Gen Y.
The good news, though, is that roleplay is a more popular and robust hobby than possibly any other time in its life. If nothing else, its considerably more acceptible in the mainstream- you need look no further than the RPG section of your local big-box bookstore for confirmation.
3Ed was a BIG part of this. 4Ed, dislike it though I do, may prove to be even more accessible to the Gen Y players than its predecessors. If so, the future of gaming as a viable industry is secure, especially if, like its predecessors, it also acts as a gateway to other good RPGs.