I think it'll be like this.
WiiU comes first and is more focused on innovating the gameplay than increasing the performance from current gen consoles. Nintendo will have 1 or maybe 2 years head start, which will give them several million units head start on Sony and MS. There will be lots of talk in media about the controls and the importance of innovating rather than just evolving. Many gamers will complain that the graphics is barely any better than on PS3/360 and says that they will wait for Xbox720 and PS4 instead. After Nintendo releases a few huge AAA hits people will suddenly "forget" about that waiting and get one.
When Xbox720 and PS3 finally comes WiiU will already have a huge fanbase, the first price drops might've happened, all third party devs will have their key franchises on it, and WiiU will at first be the lead platform, games runs at 1080p,
PS4 and Xbox720 will get ports with some barely noticabble enhancements.
At first people will be hugely dispointed in that the difference between the "true" next gen consoles and WiiU barely shows, the fanboys will talk about details in physics and particle effects and how great the games will be a few years in when the devs have learned the new systems, but in the end the WiiU titles will get better and better too and since there are no resolution differences most games will keep looking "the same" to normal people. The differences will be visable to those who care a lot about details but will only be seen as "huge" by fanboys and analysing programs, kind of like today in PS3vs360 comparisons.
Oh and WiiU will of course be the winner of the generation saleswise.