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.
As silly as it may seem, I haven't found anything in the 6th edition BRB that implicitly or explicitly disallows MCs from going to ground (unlike say, bikes and jet bikes, page 47).
Back on topic, does anyone have any more input on the questions from my first post? Particularly on the subject of forests, as they're what I'm the most uncertain about with regards to cover, especially when it comes to vehicles.