Even the rumoured "Low End" GPU in the Wii U, after modifications and optimization, will likely be able to play games on a similar level to Crysis 2 at close to its highest levels of detail with a resolution of 1080p @60fps ... While graphics can improve beyond this point, the value in pushing graphics is becomming smaller and smaller over time.
On top of the lower value, until there is a means of managing development costs while producing dramatically higher quality graphics it is unlikely that publishers and developers will push high end hardware that could be released with next generation systems. At a time where developers are going bankrupt if their $20 to $40 Million game doesn't sell as well as expected it isn't likely that these publishers/developers will want to start producing games with an average budget that is approaching $100 Million.
Edit: Please note that I'm not saying the Wii U will be able to match the output of Crysis 2 at its highest settings at launch, but more that the best looking games after 3 or 4 years will probably be very similar to what we see from Crysis 2 on a high end PC today.
