A number of unnamed developers at "major" studios have suggested Wii U's graphical capabilities are weaker than PS3's and Xbox 360's.
Speaking to GamesIndustry.biz under the condition of anonymity, one source said to be familiar with the hardware commented: "No, it's not up to the same level as the PS3 or the 360. The graphics are just not as powerful."
Another developer agreed: "Yeah, that's true. It doesn't produce graphics as well as the PS3 or the 360. There aren't as many shaders, it's not as capable. Sure, some things are better, mostly as a result of it being a more modern design. But overall the Wii U just can't quite keep up."
The article suggests Nintendo has been hampered to a degree by the cost of producing Wii U's tablet controller, meaning it's had to scale back on the capability of the console's GPU, CPU, RAM and other components in order to keep the final retail price low enough.
With its colour LCD touchscreen, the tablet controller is going to be a relatively expensive piece of kit, hence the reason consumers will only get one with each console. Wii U is expected, at least initially, to only support one tablet controller at a time, meaning secondary players will have to use a Wii Remote.
One developer also told GI.biz that they believe the PS3/Vita combo is a stronger alternative to the Wii U with tablet controller. "You can do everything with that combo that you can with the Wii U, and more," they said.
Speaking last month, Darksiders 2 game director Marvin Donald suggested Wii U hardware is "on par" with current generation consoles. "Based on what I understand," he said, "the resolution, textures, polygon counts and all that stuff, we're not going to being doing anything to up-rez the game, but we'll take advantage of the controller for sure."