I think WotC is right that economics do not justify much more support for settings. They talked about this extensively a few years back at a con and I think it makes sense. The number of people buying a "frozen north of world x" book is really low. Even past a setting and monster book, sales must drop pretty drastically.
When reissuing a setting, WotC has to consider the availability of the old material, which is usually fairly cheap via E-Bay and the like. How many would buy a new version of Slave Tribes or Elves of Athas? (Don't answer that, the collective answer will be pretty low). The vast majority of that information in those old books is applicable regardless of edition. (I use my old Dark Sun books all the time with the new 4E books)
It is important to support the world, but this can be done in other ways. Dark Sun has seen a ton of adventures released via D&DXP, Free RPG Day, Encounters, a gameday, Dark Sun Arena at Gen Con and PAX and an actual published adventure. We have seen a number of pretty good articles in Dungeon and Dragon magazines. This is a pretty good approach. The big fan can, with some effort, land a pretty impressive amount of content. I feel pretty good about my ability to run a 4E DS campaign thanks to all of this.
This sort of support did not happen for Eberon, and I think that has hurt the longevity of the setting. Then again, I am not a fan of the setting to begin with and I don't keep tabs on it.
What I would like to see is an attempt to bridge the old model and the new via content. A lot can be done with just a Sourcebook, monster book or player book, adventure, and some online articles.
For example, the horrible DS Marauders adventure could have instead been an adventure that filled in some knowledge gaps. It could have been about the veiled alliance, taking you on a tour of the city-states and thus capturing the essence of what Veiled Alliance did as a supplement (one of the best for finding the culture of each city-state!) while making an interesting adventure. Similarly, the Dark Sun Arena does a good job of capturing the feel of what is in the Gladiator's Handbook but could be quickly re-released with 2-3 more paragraphs per city and capture that supplement.