Nintendo still made large gains in Europe and Japan last gen, if they can outperform the GameCube in those two territories (and the GameCube bombed in both of those places) they can still finish with a decent userbase even if the Wii U sells exactly like the GameCube in North America.
And if that pushes Nintendo to have to try harder, to sweat a little bit, to try some new things they wouldn't otherwise -- GOOD. That's never a bad thing.
Sure as hell beats them parading into E3 2008 drunk on their own success and saying Wii Music and Animal Crossing was good enough and basically telling core players to sit down and shut up.
The fact is too, unless the PS4/720 ramp up to ridiculous levels quickly (doubtful if they're starting at $400 or more), the 3DS should be the best selling game platform for the next two years. It's the only system that really sells solid in all three major markets. So that should give Nintendo some breathing room even if it isn't as successful as the DS. 90-95 million 3DS' in profit isn't charity money.
wiiu is basically a flop in europe and won't recover, lets be realistic, gamers are just not interested in nintendo anymore.