Bear in mind that I repeat this factoid merely from having read it here on EnWorld a few years ago, and I may not be correct, or have misremembered.The problem becomes when the flavor gets inexoribly tied to the crunch. People complained about ghouls and where ghoul paralysis comes from. Apparently we didn't actually know where it came from until 2e - a decade or more after the appearance of ghouls.
The actual reason Ghouls paralyze has nothing to do with flavor at all, origin-wise. Back before D&D, in Chainmail, ghouls could paralyze. It was just one of the rules. A situation cropped up where it became apparent that a squad of ghouls could take down a larger, or more equipped, or more trained (I'm not quite sure) group of soldiers, like elves. It didn't make sense, and was a bit of a rules flaw. So elves were made immune to the paralysis.
So the whole ghoul/elf immunity thing was a hold-over from Chainmail. And the whole thing wasn't chosen for flavor purposes, but for rules/variations to make interesting wargame simulations.