To quote Stuart Bloom from The Big Bang Theory, "Okay, if you're gonna question the importance of an actor's signature on a plastic helmet from a movie based on a comic book, then all of our lives have no meaning!"
Dungeons & Dragons is Dungeons & Dragons. That's not to say that there can't be original thought in D&D products, but without the recurrence of certain themes, original fantasy is just original fantasy, not D&D, and some of us, at least, are here because we are /fans of D&D/. Not fans of fantasy roleplaying, but fans of D&D.
I can and often do develop my own fantasy stories and gaming supplements that have nothing to do with D&D lore, but why on Earth would I want to buy a product like that from someone else? I'm here for the themes. Remove the themes and it's just someone else's fantasy setting, and while I'm sure you are all brilliant people, out there in ENWorld, for the most part I could care less about your ideas. It's not personal, it's just that I'd rather use my own.
But D&D, like any other entertainment brand, is different. It has 40 years of history, stories, characters, and worlds that are a shared experience among its fans. Furthering those concepts to increase the volume of material available to those fans is not a sin. It's not even recognizably flawed as a strategy.
And what's more, and what I think Wizards is finally starting to realize, is that fandom is to some degree self-sustaining. Capitalize on that shared experience, and it brings new blood in on its own. Geeks are curious, and as they pursue the answers to their questions they become fans.