Of all the reactions to 5th D&D Basic I find this one most intriguing - that the cultural reference point in the game has shifted from external history and legend (and to be fair, a lot of 1920-1970 pulp literature) to the adventures and novels produced for the D&D game itself.
It's tempting to tell a narrative of decline. But more realistically, then as now, it's only a minority of participants in roleplaying games - especially the mass-market, first-stop kind of game that D&D has always been - who know who Ogier the Paladin was, either in legend or in Poul Anderson. When these players import cultural content from history, legend and literature, they become superior Dungeon Masters and character-concept roleplayers.
In fact, I would say there are more new players now who would know about the Paladins of Charlemagne than about the Dragonlance Saga. Say what you will about the decline of attention spans, for the young people today who catch the history and legend bug, the Internet offers a far more vast resource than anything possible when I was growing up. What's more, it's far easier to find discussions and examples of gaming design and practice online, and that is the stuff that really matters.
If my high school D&D group is any example, I was the only one who could rattle off the differences between Lin Carter's Ganelon Silvermane and John Jakes' Brak the Barbarian; who was in the library every Saturday absorbing Borges' Book of Imaginary Beings and the Macaulay castle books. We had another guy who was imaginative but more with a horror and violence bent; three guys who would go into engineering and IT, who knew fantasy and SF but not the weirder corners of the genre; and a couple of average dudes who were just there to play. But none of this cultural literacy could help me run a better game, and for all I tried to put things like historical Christianity in my dungeon, it was at the core a monster motel with a lot of pointless dressing.
Say what you will about the literary merits of the D&D canon (and the vaunted Appendix N is no Harold Bloom paradise either) -- because it sticks so closely to actual gaming, a discussion of the approach of the GDQ series, versus Dragonlance, versus Forgotten Realms actually has more direct bearing on how a DM would run a campaign. I know the actual name-drops in the new Basic document don't lead you directly there - but again, we have the Internet to point out those easter eggs for the clueless.