And this is true, but if they are able to look at the things you don't think should be in there and find good uses for them that enhance the setting in a positive way, they would be stupid to rule them out just b/c they didn't originate in 2E DS.
I'm not a purist about it. If the hammer makes sense, use it. There's no reason to give us new stats for Athasian elves if the basic 4e elf stats work fine (ditto halflnigs, dwarves, whatever). Maybe an alternate racial encounter power to re-enforce the different flavor, but whatever.
But if there's no compelling reason to use it (like the Feywild, like the Far Realm, like the Divine power source, like Eladrin, like Tieflings), there's no point in trying to force the square peg through the round hole. Probably you'll only get it halfway through anyway, and then you'll have neither a peg nor a hole anymore, you'll just have some sort of half-stuck peghole mutant that nobody can use (as, some would argue, 4e FR turned out to be.
).
With Athas enjoying the lizard/bug side of the critter palette, I see no reason that Dragonborn can't fit, for instance. Re-fluffed and maybe with a new racial power (and renamed, perhaps), they fit pretty well, and add a "lizard person" option for PC's that really would enhance Dark Sun, I think (since we've already got "bug people" with the Thri-Kreen).
IMO, extremists are for religion and politics, not so much for RPG settings.
I'm a functionalist: if it works, use it, if it doesn't work, drop it. The time and effort spent trying to make something fit could instead be spent
making a friggin' round peg.