I'm gonna have to disagree a bit on the part about it being harder to push the system -- at least if we're talking about the Wii/GC. You guys forget the the Wii/GC was disgustingly easy to program and develop for. The sad truth is that developers are lazy. They ported PS2 stuff onto GC and Xbox. Few ever bother to truly tap into it's power. Things like normal mapping, bump mapping, EMBM, light scattering, specular lighting, depth of field, indirect textures, FSAA, AF and some form of dynamic lighting are all quite possible on the GC.
Remember Factor 5 recently bitched about developers not even trying? They no longer work with Nintendo and they still know the hardware better than others. The effects I listed above will eat up fill-rate, but Factor 5 also noted that the Wii has insane fill-rate compared to the GC.
The Wii and GC doesn't use shaders, but they use TEVs. Most developers are more familiar with directx programming so shaders will be easy to use on the other hardware. The Wii/GC's TEVs are less feature rich compared to shaders, but can be just as powerful if they actually BOTHERED to try and get it to work. The GC is so well designed that it's almost impossible to get a code to run badly on it.