Nintendo recently stated on the official New Super Mario Bros. U site that the game would run in full 1080p. However, the developer has now retracted the claim, stating that the game will simply run in 'high definition'.
It has changed from:
“Experience Mario like never before… in full 1080p HD, only on the Wii U console!”
"Experience Mario like never before... in high definition, only on the Wii U console!”