I think that this part misses the point about the differences between Halo and Mario. Halo is and always has been aimed towards the types that have been long term gamers and has only been recently usurped by the likes of Call of Duty et al.
Mario and its entire universe has brand value with parents and is geared towards practically anyone who can figure out a d-pad.
While I think that most of the Mario franchise is just a rehash of a rehash (Mario Bros. Wii being the last rehash I liked), for as long as parents see the games that way, Nintendo can keep pumping them out.