That's not the problem. The problem is UE3 is designed to work with DirectX style hardware. The Wii GPU is very different from the GPUs in the 360/PS3, which are more like current PC GPUs. Epic would have to recode some of the low level parts of the engine to properly take advantage of the Wii GPU to get the same kind of effects they can get on the other systems. It's not just poly count and texture depth. It would be a lot of work, and not necessarily for any gain, since UE2.5 already works on the Wii.