It was recently confirmed that the Wii U has not been running 1080p with any games yet. This is due to frame rate issues when the game is running at 1080p. However, Nintendo has confirmed that the Wii U can definitely provide 1080p, just not efficiently right now. I’m sure Nintendo will get this sorted very soon. This is also a common problem on PS3 and 360, so don’t worry just yet.
Eguchi said the following:
At Nintendo we have different teams working on different games that take into consideration the resolution. If they think that by focusing on 720p and a certain frame rate to get a certain experience, than that’s ultimately how they make their decisions. We might consider using 1080p, but, for example, if we want to get 60 fps, at a particular stage of development, it may seem 720p is more realistic.
Wii U fans should be able to rest easy though, because many reports, as well as lots of visual evidence, have shown how well the Wii U looks when it is compared to Wii and its rivals.