The Broadway is a slow embedded PPC processor, that's fine, it serves its purpose. It's cheap to make, power efficient and small. IMO don't get your hopes up too high to think there will be huge gains in the future, it's a relatively simple processor similar (compatible) to the one found in the GameCube, GameCube developers won't run into troubles getting to most out of the Wii now and in the future.
The choice for less impressive less ambitious similar tech was a smart choice by Nintendo, they wouldn't have been able to compete on technicals anyway, this now allowed them to get the most out of the Wii quickly (like Mario Galaxy) and sell the Wii at huge profits. It also allows the Wii to be as small as a slimline PS2.
The original XBox may be more powerful overall (I imagine a default harddrive would be a big plus technically), but it was IMO a big ugly console, not as cute as a Wii.