Urgh so after the hell of STV and Tanaris, I had a nice leveling sequence in Ferelas and Hinterlands.
Now I've hit Searing Gorge and it seems like that's where the moron zerg went next, all the Dark Irons are dead. That's shit since there's lots of excellent quests there.
So looks like they know how to travel south from Undercity, to Hillsbrad and Arathi then Searing Gorge since those zones were busy, but they can't find the entrance to Hinterlands since it's fairly quiet there.
So my thesis is that retail players don't know that Swamp of Sorrows/Blasted Lands, Desolace/Ferelas and Alterac/Hinterlands exist. Fingers crossed that Felwood/Winterspring are similar.