Primitive building methods take longer than modern more advanced ones. Almost by definition. I don't buy for a moment that Deathwing attacked and a month later Org is rebuilt. The time it takes to gather the materials, treat the wounded/traumatized, get the builders and implement everything alone would take a month.
I'll accept whatever Blizz tells me it is, be it a month (retarded) or a year (sane and rational time frame). I've had to swallow all sorts of dumb things to fit into the lore :P
Well, I was more thinking along the lines of how the Horde has been in Ashenvale for a damn long time without cutting down any more trees (to us), and then the Cataclysm hits and everything is fast forwarded and more trees are down. So obviously there was enough time for them to get the materials, and they probably always had the peons available to build everything quickly.
I think the problem really is that we "live" in a static world, so we don't really see things getting done gradually over time, so we take it as kind of a shock when things are different. I'd rather like to pretend that the stuff was already in the process of happening.
After Thrall saw the construction of stuff like Warsong Hold and Conquest Hold, he thought "you know what, that stuff is pretty awesome looking", and so Garrosh was allowed to have that stuff done for Orgrimmar. It would be kind of interesting to see if eventually that style hits Thrallmar and the other Outland buildings. :P