Mercurius
Legend
Because the world it which most D&D games take place is not the real-world.
This is why many gamers eschew the concept of 'realism' and instead describe this as 'verisimilitude' or 'internal consistency.'
In the game-world implied by the game-mechanics, those who wield magical power granted by the gods cannot use any but blunt weapons. It's one of the many ways in which the game-world differs from our own.
Speculative fiction takes our world and changes a number of elements to create a different world. This is one of those changes.
Maybe I misunderstand you but the way you describe "the" D&D game world is as if it is one world with a codified set of "verisimilitudinous" themes and tropes that should not be varied from; e.g. clerics must always on use blunt weapons, elves have weak constitutions, etc.
Alternately we could look at "the" D&D game world as a kind of archetype from which there are many possible variations. The published D&D material--from the OD&D stuff of the mid-70s to the latest Dragon article on D&D Insider--could be seen as a vast and detailed toolbox that an individual DM can populate his or her own world with (or craft his or her own version of a published setting with). So there can be many, infinite really, possible variations, with a range from "classic D&D" settings to more wild and wooly exotic settings.
I think this is an interesting observation/insight. His whole return to a simplified rule system in Lejendary Adventures makes it seem like Gygax was in essence saying, "Given the choice, I'd rather let a competent GM decide what happens than the rule in the book."
However, between AD&D and LA, Gary designed Dangerous Journeys (Mythus), which wandered into the insanely complex.
Yeah, this is interesting to see, isn't it? EGG went through a trajectory of:
OD&D -- > AD&D (including Unearthed Arcana) --> Dangerous Journeys --> Lejendary Adventures.
It was almost as if he boomeranged way out there with Dangerous Journeys in terms of rules complexity and "simulationism" and then started back with LA.
This doesn't mean his particular trajectory is "right," it just is what it is.