I think they're making a decent effort based upon the software they have. First, the one Wii U ad i've really been seeing puts all its emphasis on NSMBU, which is important, secondly it emphasizes the capability to go up to 5 players, or down to one player who is playing off-screen.
It is somewhat of a more complicated sell, but if they keep hammering away at the idea that it can do both (more local multiplayer and off-screen SP), it should help get the idea out there.
Of course, it's all about the software to back that up, which is why NSMBU will be good at selling the concept, because of heavy co-op multiplayer, but also it's a simple enough game to reduce to the gamepad more easily.
If anything, they're not promoting Nintendo Land enough.
Monster Hunter: pissing me off since 2010.
