Hehehe... Apparently, the causes of the Wii's success are now as shrouded in the mists of time as those of the Crash of '83, Leo.
I'd wager that, more specifically, Bowling on Wii Sports sold more than its fair share of Wii systems. I can't really recall anyone raving about any other games on the disk, to be honest. Heck, even non-gamers enjoyed that one a good deal.
In regards to less than spectacular Wii U sales, Nintendo needs to get their heads out of their arse and put out a demo kiosk in stores that has actual demo games to play rather than just two minute game trailer videos for prospective buyers to idly watch. This puzzles me. Are these lame kiosks just specific to my area or are they a pan North America marketing mistake?