I'm guessing partly by having a reputation for creating classic titles exclusive to their machine core which anyone with more than a passing interest in games should have experienced. Also by having a unique control system which adds new unique features to ported titles.
I figure through targeting younger/causal gamers with the wii they sort to develop their own core gamer base. For example Nintendo Land being showcase and practice area for a range of their key titles.
Once the next gen race gets going they can drop the price to build a user base of gamers looking for a reliable machine which fits more easily into their life (off screen play) and attract 3rd party developers by having a plenty of users.