D&D has an implied setting with elves and dwarves and paladins and happy munchkins dancing and singing in the woods. For a large number of settings, that works fine, because all these things are part of them. For some, what you take away is just as important as what you add.
Even a relatively generic setting like Dragonlance would suffer in terms of flavor, identity and atmosphere if it were given the Eberron kitchen sink treatment, and forced to have orcs and drow etc., let alone Dark Sun, where exactly what you don't have (weapons, water) is often the focus of the game!
It appears from what I've read that WotC has pushed a couple of simple solutions to problems which often work, but would probably be better dealt with on a case by case basis. You probably know them, here's a couple:
1) Crunch good, fluff bad.
2) Options good, restrictions bad.
On the surface of it, they sound fine. Progressive and practical. However, one shoe size doesn't fit all, and products like Deities & Demigods and now Dark Sun prove exceptions to these rules.
EDIT: There's probably some of WotC's fear of splitting the game audience in there somewhere as well. Exclude paladins from a setting and you can't sell those players a paladin book.