The Wii sold because of Wii Sports and the Wii U will sell at first because of the Wii. Effectively the big system seller for the Wii U will be the popular Wii titles like Wii Sports.
I agree with that. I believe that this could be the key for the very first months after launch, after that WiiU will need real system sellers.
I'd have agreed with this in 2010 but WiiU is coming out far too late to capitalize on Wii's popularity. iOS/Android are what's popular now.
The last Wii titles of any significance was Wii Sports Resort which was, for the mass audience, an eternity ago. Wii Music, Wii Motion Plus, Wii Party and the poor upgrade value of Wii Fit Plus have failed to maintain the brand's relevance IMO. Sadly Wii Fit U is a launch title and from what we've seen, really doesn't look anywhere's near different enough from Wii Fit/WF+ to justify a purchase of the game, let alone a new system to play it on. Or to resusitate a now tired genre.