Why Vancian magic is "Vancian".

"The tomes which held Turjan's sorcery lay on the long table of black steel or were thrust helter-skelter into shelves. These were volumes compiled by many wizards of the past, untidy folios collected by the Sage, leather-bound librams setting forth the syllables of a hundred powerful spells, so cogent that Turjan's brain could know but four at a time.
Turjan found a musty portfolio, turned the heavy pages to the spell the Sage had shown him, the Call to the Violent Cloud. He stared down at the characters and they burned with an urgent power, pressing off the page as if frantic to leave the dark solitude of the book.
Turjan closed the book, forcing the spell back into oblivion. He robed himself with a short cape, tucked a blade into his belt, fitted the amulet holding Laccodel's Rune to his wrist. Then he sat down and from a journal chose the spells he would take with him. What dangers he might meet he could not know, so he selected three spells of general application: the Excellent Prismatic Spray, Phandal's Mantle of Stealth, and the Spell of the Slow Hour."
-"Turjan of Miir", Jack Vance

And there you have it. Many works of pulp and fantasy inspired the tone, setting, creatures, and flavor of D&D, but as far as I know, this is the only one that was turned whole-sale into an actual game mechanic. This may be because most of D&D's game mechanics were a direct descendent of the wargames the creators were constantly playing, and adding rules for magic to the mix was really the only thing they had to come up with from scratch.

Interestingly enough, Vance's wizard's were also Men of Action, as opposed to the more scholarly and frail presentation of the "traditional" D&D wizard, more akin to the rough and tumble "scientist" of 50's B-movies, who always seemed to shoot several martians and get the girl in the end. Though I can't recall any stomping around in plate mail, a sword was always carried, lots of running and jumping and fighting were usually involved, a bit of thievery and confidence trickstering, and a healthy dose of drinking and wenching. A modest collection of magical trinkets and instruments was also desirable.

I wonder how different D&D would be today had its creators been more influenced by the magic "system" of a Piers Anthony, Michael Moorcock, Katherine Kurtz, or even Robert Jordan (eek!). Luckily the one they picked lent itself well to the environment of gaming, and is a large part of D&D's staying power over the years. Even though I tinker with different magic systems from time to time, you can't argue with Vance's simple and elegant system, and the gamist enjoyment of successfully plotting out your spells ahead of time for a mission.