http://www.wizards.com/files/367_Ecology_Genasi.pdf
After reading the above, I lost any remaining goodwill I had toward 4th edition. If 4th Edition once had the privilege of my benefit of the doubt, this must surely be the final nail in the coffin. To be honest, I was irritated enough with the homogenisation of tieflings into one, indistinct mass. In a way, that was fair enough, since tieflings could be rendered like a kind of concept: redemption, rebirth, a new identity for a new world and so forth. But grossly generalising genasi irrespective of elemental heritages is simply lazy.
No, I'm not an odious purist - to the contrary, I think artistic license goes a long way in fantasy, but there is simply no excuse for dumbing down, laziness and poorly written banalities. Which is precisely why I try to give genasi, when and where I can, fair treatment both when I run Planescape and when I write for this site (genasi play a prominent role in my latest article) and others. Conversely, if there is any flavour, brio or verve in 4th Edition, I have yet to see it.
Rant over. Shall return to my life now.
Everything's simplified in 4e. I do find it wearing to have everything credited to the same handful of origins (the primordials, the gods, the Far Realm, Bael Turath, the fomorians) again and again. In 3e, a creature might be from outer space, a parallel universe, any of dozens of planes of existence, the distant past, the future, a reality that no longer exists, a wizard's experiments, or any number of imaginative possibilities, while in 4e it almost always boils down to those five (the only exceptions I can think of are certain creatures of shadow and the obyriths... I suppose hobgoblins and drow also constitute separate origins - and I was very happy to see obyriths given a relatively fresh origin, although Demonomicon was for the most part just a rehash of previous material awkwardly shoehorned into the new cosmology. At least they managed to fit most of the previous material in, something I was dubious was even possible in the reimagined Abyss. We still lost the War of Ripe Flesh, one of James Jacobs' cooler ideas, and the consequences of that war like Malcanthet, Red Shroud, and Lynkhab).
But, of course, that's 4e core, and the point of core (as a point of entry into the game) is to be simple, while individual campaign settings can be more complex. And the Planescape and 3e books (and websites) still exist, regardless of what WotC does.
And some of WotC's designers still manage to come up with some very cool concepts even straightjacked by the extremely limited palette they have to work with. Comparing current 4e core to what TSR was churning out during various dull periods, I think they're significantly better, and the average quality of 4e books is significantly better than the average quality of 3e books. The quality of generic "core" fluff in 4e is better than generic "core" fluff in previous editions, which mostly relied on setting-specific material (Planescape, Forgotten Realms, Spelljammer, Greyhawk, Ravenloft, Dark Sun, etc.) to be any good, outside of Dragon Magazine and the like.
As for genasi, I really like treating separate flavors of genasi separately (and even different families of fire genasi might have very, very different histories). That said, there really hasn't been much development on genasi outside some relatively brief notes in the Forgotten Realms setting listing possible origins for them on that world, so it's not like the 4e genasi are replacing anything that was terribly developed. As the history of a single type of genasi, or perhaps a replacement for ruvoka, 4e genasi aren't bad.