How on earth do you consider the Wii noticably more powerful than Xbox? The xbox had high resolution graphics upto 1080i resolution, 32bit colour not 24bit colour, true 5.1 sound, a more advanced gpu, a faster cpu, 64meg of main memory not 24meg plus 3 meg video, a built in hard drive with the ability to cache in extra game data quickly. How are you gauging the Wii has more power than the Xbox? I've got both and the best Xbox graphics easily beat the wii. Games like Soul Caliber II run at 720p on xbox. Some games run at 1080i. Have you actually seen Far Cry on the original xbox? Still a stunning game visually.
The 64MB of unified memory within the Xbox was for everything while the 88MB on Wii is split. The unified memory is superior that's certainly not something I'm arguing, but if you think all that 64MB is for GPU work you need to do more research. On average I doubt Wii has less memory available to the GPU, and at the resolutions used by the Wii it really doesn't matter. Wii's GPU however is superior in some ways to the Xbox while inferior in others. Overall however the Wii is more powerful than the Xbox its not even arguable. The only significant advantage the Xbox had over the Wii is programmable shaders. A hard drive hardly has anything to do with the capabilities of a console so that's a mute point. Developers choosing not to really push the Wii really doesn't make this any less true. I'm gauging the Wii's power based on info that's been found by various sources. You have to realize that in real life applications the Xbox wasn't extremely more powerful than Gamecube and the enhancements to the architecture from Gamecube to Wii as lack luster as the console was surpassed what was actually capable on the Xbox.