Okay, so, basically you're all saying that D&D is its own unique genre/style of fantasy, and it doesn't model other genres well. Except that some claim it's perfectly easy to tweak, but Core D&D is the game most gamers like.
Maybe that's true. Maybe D&D is the way most D&D gamers like it. I certainly enjoy playing and want to keep playing. I'm perfectly capable of tailoring the game to the genre that I want. But I also want to see the game survive and grow its audience. And if the game is going to survive, it's going to have to attract new players - that is, people who have never played D&D before.
One argument that's been floated is that Core D&D has trouble attracting players because it's too "rules-heavy." Given the good, but not runaway, success of products like Castles and Crusades and True 20, there's a certain segment that feels this way. The D20 system is designed to be easy to learn in play, and, in my experience, it is. Play through D&D (or ANY d20 system game) once and you can learn the basic mechanics of the game. So I'm wondering if rather than the rules getting in the way, it's the genre conventions (D&Disms) that present the "barriers to entry" for attracting more players to the game.
Is the Core D&D concept universally appealing? Do people just "get it?" Again, maybe. Maybe D&D hit some kind of sweet spot in our mentality that it has near universal appeal and the real "barrier to entry" is people willing to become "gamers." So even though fantasy as a genre is experiencing a popularity boom in pop culture (Harry Potter, Lord of the Rings, Pirates of the Caribbean), the game can't really benefit from it.
Maybe that's the case. No game OTHER than D&D has ever had its distribution or brand recognition, so the chances of any other roleplaying game cracking this nut is pretty slim. So what I'm suggesting is that maybe the game's conceits have marginalized its appeal.
I think I heard that Lester Del Rey used to say that he would allow 3 outlandish assumptions from a science fiction author (fantasy was included on this list). His reasoning was that any more than that and a large portion of your potential audience wouldn't "get it" and therefore, wouldn't buy it. As sci-fi as a genre developed, there were certain "genre conceits" that became "gimmes" with the audience. So they don't have to be listed in your "outlandish assumptions" - they just are.
To put it mildly, D&D now has WAY more than 3 assumptions built into it, over and above the "genre conceits" of high fantasy. Like I said, maybe I'm off-base, but pending the runaway success of a "rules-light" D&D, my money's on the larger potential audience having an issue with the assumptions of the game that are built into the Core Rules.
And like I said, given the issue of "brand recognition" ONLY D&D itself can tap into this audience.
Sorry for the long post.