Short-term (enough to count overall) the Wii won because of Wii Sports and some of that Nintendo brand strength.
Long-term the Wii lost, because they stopped making games for it.
Where is the Wii Sports for Wii U? That is the big question that will determine how it does early in its life-cycle with the casual masses going crazy for it or not. The later part of life cycle will really depend on whether next consoles from MS/Sony command exclusive 3rd party interest/support and don't bother porting those games to Wii U. Keep in mind, MS/Sony wont just have to offer significant leap, they would have to do so without a big price hike.
On other hand, if the difference is not that significant, than even with MS/Sony next-consoles being able to push more tech-specs, 3rd party developers will treat the Wii U as the base platform like they did with PS2 back then. In that scenario, Nintendo wins the full life-cycle.