So far as I can tell, Monstrous Creatures no longer have vehicle-esque cover rules; they are treated as standard models for purposes of determining cover. Yes, this means MCs get cover simply from being inside of area terrain.
That's the way I read it too. MCs are more flexible then vehicles. Sure they can't go to ground but they can hunker behind the remains of a building.
"Fetch me another plaything. This one seems to have broken." -Urien Rakarth
Space Marine- "This planet is ours, witch."
Eldar- "No ... This planet is theirs ..."