Lord Mhoram said:
I hate books that give lots of social or racial backgrouns, because then the writeups reflect that, and maybe I don't want the Orcs in my world to behave that way, and have that background.
I love 4th for giving that stuff back to the GM.
First of all, 4th edition's three core books contain a much more specific assumed world than the three main 3rd edition core books did. In earlier editions tieflings were beings who vaguely had fiendish blood, while in 4e they're descendants of the noble caste of the fallen empire of Bael Turath. The 4e MM has specific creation myths for beings like giants, the dragon deities, angels, an elaborate description of the Nine Hells - a lot more campaign-specific detail than any previous Monster Manual had. It specifically tells us that humans have no great empires, and hobgoblins had a kingdom which is now destroyed, and halflings all live on rivers.
So, what I think you meant to say was "I hate 4th for taking that stuff away from the GM."
More importantly, though, is the fact that that stuff has always been and continues to be ultimately in the DM's hands no matter what the book says. Would you rather tieflings had a different origin, or that humans and hobgoblins had vast empires that still exist in the present day? Change it. The existence of copious amounts of flavor text does nothing to limit your own creativity, but it certainly can inspire it, either to build upon it or to introduce variations.
More flavor text is thus nearly always a good thing.
Now. That said, the 2nd edition books still set the record for most amount of detail on habit/society/ecology in their entries, but most of this is very generic and not specific to any particular world. 4th edition may give slightly less detail in total than 2e (but generally more than 1e, I think), but the
kind of detail is much more specific to a particular assumed cosmology and in-game history.