Nintendo have removed the text, it now reads:
Experience Mario like never before... in high definition, only on the Wii U console!
1080p is still perfectly feasible. Mario in 1080p will be a landmark in gaming, regardless of what some of you may think. Nintendo may well wish to announce such news in a more fitting manner.
It would seem Nintendo have been hard at work since E3. Do you remember how their representatives said all first party titles would run at 720p only, well now it seems that's not the case, starting with New Super Mario Bros U. According to Nintendo's newly opened official site for the game:
Experience Mario like never before… in full 1080p HD, only on the Wii U console!
I hope this is true and not merely a mistake. I also hope Pikmin 3 follows suit. I know the game looks gorgeous already, but it's still something I think most fans would want, if it can be pushed in such a game (originally designed for Wii).