I doubt Libris Mortis and the 'locale' books (the one about desert and on the sea, ec) did very well with the mixture of PC and DM information. While it would conceivably have "something for everyone", it just made it generally useless. 4e books may be trying to be "better for the buyer" to encourage them to buy, since the attempts at making books that everyone can use may have ended up with books that no one bothered to use.
That's true for me, as well. And I don't even play 4E (yet)!I'm probably buying MORE than I did in previous editions.
These days if I'm buying a book it's for the flavor.
I actually wish a 3pp would put together a campaign system that's crunch free- Just GOOD solid flavor. Instead of designing new classes and fats and powers, just use the existing classes and such and tell me how they fit in the game world.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.