Well thats just the thing, aint it? Pandaria, Warlords of Draenor, Wrath of the Lich King... All these expansions were self-contained in where they took place.
But Cataclysm dealt with the blows and aftermath Deathwing had dealt to the world, so those things took place all over the map. Hyjal in Northern kalimdor, Uldum in Southern Kalimdor, Twilight Highlands in Middle Eastern kingdoms, etc.
What's more, Cataclysm doesn't seem to be an option for Chromie Time. So I imagine, if you choose Classic, you'll be levelling from 40 to 50(?) in the Cataclysm area thats the most 'natural' progression of where you were when you hit 39 in "classic" zones.
I mean hell, Cataclysm aint even an option here, leading me to further believe this is the case:
... Because the other option would be all Cataclysm zones never seeing use again.