AD&D has all that too, but instead of "this is the god that made elves" we had "this is the god all elves explicitly worship in this specific way because that's what elves do" in this world".
All around though, implicit setting is something that infects D&D specifically. I'm hoping they'll move away from implicit in the future.
That's the thing though; the fluff/crunch divide is a relatively recent invention. There was no discountable fluff. If it was in the book it was a rule.