One thing that's going to really help the Wii U is Nintendo's surprisingly forward thinking with their choice of architecture. It's going to be easier to port between the Wii U/PS4/720 than it currently is to port between the Wii U/PS3/360. The architecture of both the PS3 and the 360 is a bit odd with floating point work being done by the CPU rather than the GPU, and this generation we're going back to normal with the floating point work being done by the GPU.
Developers are also going to be greatly helped by both the Wii U and 720's memory setups being virtually identical. I really can't understand why Sony didn't go the same route tbh. They would have ended up with 8GB of RAM with much lower latency and using less chips making the motherboard a hell of a lot cheaper to produce as well as the RAM chips themselves being cheaper.
Another thing going in the Wii U's favour as far as development is concerned is that any interaction between the CPU and GPU is going to be lightning fast.







