Quickleaf
Legend
n/day has always been a mechanic of convenience. When EGG settled on Vancian, it wasn't to emulate the fiction of Jack Vance, it was to give magic-users a "relatively short spoken spell" they could cast practically, do something effective, without overwhelming everything else. (It didn't work, magic-users still dominated at higher levels, but that's what he was going for according to his own commentary in the 1e DMG.)
Vancian 'memorization' was dropped for preparation then un-explained spontaneous, now all casters are spontaneous and the memorization/preparation narrative explanation of slots-per-day is gone.
Really? I had no idea about that tidbit of gaming history. Was that from your personal conversations or from a book or something? I always assumed it was because Gary was a fan of Vance's portrayal of magic.