My impression is that its graphics capabilities are not far beyond the current competition. That is probably plenty enough power anyway, but at the same time they don't want to reveal specs because people would judge the system on the fact that the specs are similar to five year old products, despite that you shouldn't.
We're rapidly approaching a threshold where graphics across the board are going to be impressive and they simply won't matter anymore. There will still be improvements, but they won't be defining systems like they were a decade ago, when everybody was debating what system had the best capabilities.
The industry in the modern era is about marketing, software, and services. Hardware matters more in form than raw tech specs.
What's most important about Wii U on the technical side is its architecture. Work on the system to an extent carries over from the current generation. Don't expect visuals of Wii games to get much better than you see in their first year. Developers already know how to achieve results with the hardware because they've worked on the Xbox 360 for years. Of course they aren't identical, but they're going to find all the ins/out/tricks a lot faster this time.
Your impression is quite off then. Both demos to some degree showcased effects simply impossible to replicate with current generation consoles. That's without mentioning that both demos where running at 1080p native resolution in real time while pulling off Global Illumination, high quality textures, and ext. Literally only a few PC games on their highest settings can do some of the things being done in both demos. The more impressive demo the Japanese Garden Demo is specifically stated as being based on an older version of the hardware and Zelda tech demos always are worse than the final product. Their choice regarding the demos perhaps wasn't the best. It would of helped get the capabilities of the console around to specific crowds of individuals if one demo had been a realistic urban setting (a FPS ext). We've more or less already meet the threshold where most individuals have a hard time telling several of the current improvements in graphics compared to the capabilities of the current consoles. That has a lot to do with the fact majority of it is very subtle and that no developer has really embraced tessellation. What improvements can be seen for next generation consoles also really need to be seen in person or the original video files as recordings lose quite a bit of detail.