That said, I would argue that the divergence that can be seen so clearly in the WotC editions began much earlier. Consider that, in the justly famed Appendix N of the AD&D Dungeon Masters Guide ("Inspirational and Educational Reading"), Gary Gygax explains:
The following authors were of particular inspiration to me. In some cases, I cite specific works, in others, I simply recommend all their fantasy writing to you. From such sources, as well as just about any other imaginative writing or screenplay you will be able to pluck kernels from which grow the fruits of exciting campaigns. Good reading!As you can see, Gary wasn't closing off possible sources of inspiration to only a handful of books or authors. He was, throughout his career, committed to taking inspiration from wherever one might find it. At the same time, Gygax made clear which authors and books were the primary influences on him as he created D&D. It's these pulp fantasy books and authors who form the game's "literary DNA" and are the ones most consonant with the game as one of its creators conceived of it. (A similar list written by Dave Arneson would be intriguing indeed)
The DMG was published in 1979. Just two years later, Tom Moldvay's Basic Rulebook includes a lengthier bibliography, entitled "Inspirational Source Material," which was compiled with the help of Barbara Davis, children's librarian at the Lake Geneva Public Library. Moldvay states that
Books on folklore, mythology, fairy tales, bestiaries, and knightly legends can often help the DM fill in important details of a campaign, but fictional tales and fantasy novels usually provide the best sources of inspiration. The following list includes some books which might prove useful.The divergence is clear. Whereas Gygax's list was a list of the specific books and authors who influenced him in creating the game -- and are thus a window into how he saw the game -- Moldvay's list is a generalized quasi-academic survey of fiction and non-fiction that might hold some interest to players of D&D.
It would be foolish to claim that Moldvay's list is the cause of the shift in the perception that D&D was a "generic" fantasy RPG without very specific inspirations and antecedents. Rather, I think Moldvay's list suggests that, by 1981, either enough gamers already believed this to be case so that including a reading list so different in tone from Gygax's was uncontroversial or that TSR was making a concerted effort to shift the game away from its literary origins in order to broaden its mass market appeal. The truth, I suspect, is somewhere in between. I certainly have an abiding respect for the memory of Tom Moldvay, whose work on modules B4, X1, and X2 reveal him to have been a keen student of pulp fantasy. Likewise, as highly as I regard TSR's products between the years 1974 and 1983, it's not as if the Golden Age ended abruptly and without the gleeful assistance of TSR itself, which made a number of creative decisions that laid the groundwork for the gaming world that exists today.
This is not a matter of "Gygax good/Moldvay bad" and I resist any attempt to characterize it as such. Nevertheless, it's hard to deny that the difference between the two reading lists reveals a shift in emphasis and approach that has had consequences for decades to come. Despite that, I feel compelled to say that, for all their differences, the fact that both Gygax and Moldvay saw the need to include a reading list at all shows how different they both were from the way the hobby would develop subsequently.