Even if the market realities haven't changed, there are ways to tie the settings in with normal products so that people who wouldn't ordinarily be interested in the setting might make the purchase. For example, if you put out books of mostly crunch and some fluff - let's assume the 4E Psionics Handbook, 4E Bo9S/Oriental Adventures, and the 4E Book of Vile Darkness - you can put out each book with rules to run the concepts and fluff to help to integrate the new rules into the existing setting / assumed PoL setting.
However, if you put out a new setting book roughly conciding with each of these, you can piggyback on them with settings that take those rules ideas and put a spotlight on them or extend the ideas to their logical conclusion, along with some setting-specific crunch that expands on interesting ideas in the core books.
So Dark Sun or Eberron might be tied to the Psionics Handbook, and might generate more sales. Similarly the Bo9S with Kara-Tur and BoVD with Ravenloft. I can guaruntee it already happened to an extent with psionics and Eberron and, earlier, high magic and the Forgotten Realms. I know that I bought the early FR books for just that reason when I woudn't have otherwise.