Desdichado
Hero
Sure. And I really like the D&D take on Orcus and Demogorgon, for instance, which otherwise are pretty generic mythological figures without much to recommend them.I must respectfully point out that the back stories everyone here seems to regard as an intrusion and as disposable fluff, are what many fans considered an indispensable element of what they LIKE about D&D and made the game attractive to them in the first place! D&D is not a fantasy version of GURPS, and people shouldn't try to make it fit that mold. Hussar would probably LOVE GURPS - nothing but character/monster creation rules and zero backstory. But I believe that the reason D&D has outlived so many imitators is precisely because of STORY... backgrounds that make the game come alive. Don't think so? Look at the outcry when 4e ditched almost every traditional piece of lore and substituted a new background and a new set of planes. Planescape fans weren't the only ones crying foul. And the lore about the demihuman deities goes back further than "Monster Mythology", FYI... at least as far back as 1e's "Deities and Demigods". For many players and dms, the story of the epic fight between Correlon and Grummush is as much a core part of D&D as character classes and spells.
But at the same time, the degree to which D&D manages to accommodate everyone's own game is key to it's success. You say that the "story" of D&D is why D&D has outlasted so many competitors? That's an odd claim, given that almost every other RPG out there has a setting inherent with the game moreso than D&D. If a setting is the selling point, then you shouldn't expect to see D&D outlasting all of its competitors, you'd expect to see the opposite. The setting isn't what makes D&D successful--although I'll certainly grant you that some very vocal gamers do like it cough cough Shemeska cough cough--but I believe that the key to D&D's longevity is actually the degree that it manages to untie itself from those assumptions and allow gamers to use their own assumptions without having to do too much work to do so.
To the extent that the default assumptions grow, D&D will be less useful to more and more gamers.