If it doesn't get released because a carrier decides to hold it back for some strange reason his assumption is still incorrect. Tango is not "targeting only new devices in emerging markets"
You're making a category error here. Thurrott was talking about Microsoft's intentions with respect to Tango. I don't see why Microsoft can't add a few features to their OS while still targeting it primarily at new devices in new and emerging markets. But that's just Microsoft's intentions. AT&T and Nokia or Samsung or HTC may well have other intentions towards it - such as using it as a sop to the owners of their current devices a few months before Apollo rolls out and the world passes them bye.
-EDIT- ATT has committed to a post 8107 update already...
But to which devices? All of their devices? Even if they say all devices what does "all" mean? All the ones they've ever sold, or all the ones they're selling now? Or only the ones they're selling at the time of the Tango rollout - which may mean only the 900 and Titan S get it?