The game which will matter most to set the tone for the Wii U will be whatever game Nintendo decides to bundle with it (if any). Nintendo usually bundles a game with their console at launch (the N64 and GC being exceptions) and this game goes on to set the tone for that system for the rest of its life. With the NES, that game was Super Mario Bros./Duck Hunt; with the SNES it was Super Mario World; and of course with the Wii there was Wii Sports. The NES and SNES were known as the Mario systems because Mario was the pack in game everyone who bought the system owned immediately from day one of purchase. Maybe part of the reason why the N64 and GC did relatively poorly is because they didn't have any pack in title at launch, so they weren't associated with anything in particular, so no tone was really set for their image.
When you look at what Wii Sports has done with selling the system to people who normally have nothing to do with video games like soccer moms and the elderly it makes sense that Nintendo would have every reason to want to repeat that success by bundling something similar in with the Wii U. They already decided they are going to keep the Wii brand name going and are determined to continue to win over the casual market, so why wouldn't they? So I have every reason to expect there will be a Wii Sports 2 or some casual tech demo thing like that to show off the Wii U's gimmick to elderly people and nongamers. I don't particularly want that to be the tone set for the Wii U, but I believe that's what is going to happen. All signs seem to suggest that will happen. I'm just hoping that in addition to that obligatory casual pack in, Nintendo decides to also include a core game pack in as well. If you think about it, the SMB1/Duck Hunt cartridge that was packed in with the NES was sorta like that. You had Duck Hunt with the Zapper which was sorta like a casual game of its era, and on the same cart you also had Super Mario Bros which was a hardcore game. So you had a pack in which catered to both crowds. Maybe its no coincidence then that the NES was basically Nintendo's Golden Age. It was their best selling (until the Wii) system of all time, and pretty much a monopoly. It catered to everyone, so it deserved that status. Even though the Wii might have sold more, the Wii doesn't have what it takes to reach that same level of glory.