I kinda think that WotC haven't heard of the Lord of the Rings. What sort of genuine fan of fantasy would want robots (warforged) and psychic powers (psionics) in their novels and games? Tragically, D&D has been entrusted to sci-fi wannabes.
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And of course, just like all the psionics arguments, the exception justifies dismissing the rule completely, yes?
It's a matter of scope. There's cthulhu mythos elements in the odd Conan story as well, or so I gather, but it's not a core theme of the setting. When aliens invading becomes an everyday occurrence on Hyboria, with Conan fighting greys as often as picts, then you might have an argument. Until then, it's the "Greyhawk is the wild west because Murlynd has six-shooters" argument - one that crumbles under more than trivial scrutiny.
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LOL. Long after those books are forgotten, there'll still be legions of fantasy fans reading LotR and the Conan stories.
Right.
There is more under the vast roof of the Greathall of Fantasy than elves, dwarves and barbarians.
You'll find psionics and aliens (if not extraterrestrial, then extradimensional-as opposed to extraplanar) in a variety of classic fantasy literature by important and revered authors like Vance, Lee, Lieber, Lovecraft, Moorcock, and Zelazny.
Maybe its not YOUR taste, but those tropes have long and distinctive histories all their own- back to the dawn of modern fantasy literature in the early 20h century- and are no more likely to fade into obscurity than the legacies of JRRT or Howard.