I'd argue that DnD (referring to the new edition here) does use a setting: essentially western sword and sorcery that builds upon previous editions of the same game. It gives you exactly what you expect from the DnD brand, along with universe building things like the planes and the baggage that is carried along with it. Classes do their iconic stuff that we expect them to do and so on. The writers even try to tie everything together in a multiverse. Sure, its to try and sell the other campaign books if they ever release them.
I find needing 2 books as something that can work well. I don't really want too much information in a single volume, especially if that information isn't usable for players. If you could move GM material to another book and even lower the price of the player book, I'd be all for that. OH and add a starter version that includes bunches of cool stuff!