Excising the old influences from the future of D&D would be a mistake. Older does not mean irrelevant, and has been pointed out a number of times upthread, you don't want to alienate those people who grew up with the older references. Makes sense to me. Consider that aspect of my argument retracted.
However, you cannot tell me that support for games reflective of newer media and stories and such doesn't belong in D&D, or should be relegated to splats (as someone mentioned upthread, not sure who or where). As players of psionic characters know, having your stuff relegated to a splat is largely analagous to it being among the largely-ignored part of the demographic. Whether that's true or not is irrelevant - that's the perception.
To the idea that the game shouldn't change based on the whims of current culture - ya, I can see that argument. But there is an underlying current to media, general sentiments you can pick up on if you expose yourself to enough of it that are reflective of changes in the next generation's thinking. Arguing that new things like Avatar or Harry Potter are fads that will fade from the cultural conscious in a few years is facetious - undoubtedly a large portion of the works in Appendix N are almost completely unheard of today. Sure, some references are still present (LotR, as probably the most obvious one), but I'd be willing to bet that a large percentage have since faded from public knowledge, because they were - essentially - fads.
If the issue is that D&D has become so self-referential that you can't modify or adapt or even just outright add new things to account for cultural change because it would be disruptive to what D&D is, then... D&D is doomed to failure. Maybe not now, maybe not twenty years from now, but it will die. The question is no longer one of "if," but "when."
There is something to be said for remaining true to your roots. Holding on to the traditions that have made D&D what it is isn't a bad thing, necessarily. But it is if that comes at the expense of growth, of change, of adapting to the cultural environment in which new gamers will be coming to the fore, then the future holds only stagnation, and D&D will be - at some point - forgotten.