The architectural difference between the Wii U and the PS4 is minimal even if the PS4 is more powerful. The difference between a Wii U and current gen is huge though, even Nintendo who never comments on power says that it will probably be able to double the current standard and that their architecture is similar to that of the other next gen systems will offer.If you consider the current games for Wii U VS current games for 360/PS3 that could be right, but compare the Wii U's graphics demo with PS4's graphics demo. Either Sony made a very poor job in presenting the PS4 superiority or the PS4 is really all not that powerful. Just look at the Wii U's graphic demo, it looks amazing. The PS4 graphics demo looks better but just slightly in my opinion.
And for people who keep judging the Wii U graphics, remember that the 3DS started off as resembling Gamecube's graphics, but now it is getting close to PS360 graphics. Just search youtube for a RE 5 vs Revelations comparison
The PS4 just like the Wii U is GPU oriented with GPGPU functionality to compensate. How big the gap will be between the next gen systems we don't know but comparing the Wii U to 7 year old systems is laughable. Devs have had kits for 6 months, pretty much all games on the system have been quick ports, wait until we see next gen multiplats or at least Wii U exclusively developed games. Expect games like bayonetta2 to be better at showcasing what it can do.
The PS4 event had PC versions of games running, the hardware still is in development, I mean we didn't even get to see the main unit.