On an unrelated note, nvidia continues to be the market leader, despite not having taken similar approaches towards memory bandwidth. Or at least that's what happened with the ring-bus, but if we just go by press releases, then bitboys had market leading technology too. (I do prefer ati cards and tech btw, but nvidia has shown they can perform just a bit worse and beat ati to market by 6 months, and the advantages of ati's memory controller and higher bandwidth have really only shown themselves with AA enabled; the 9600 pro kicked ass even with a 128bit memory bus)
Maybe it was important for compatibility,and I'm not talking just games but game engines designed around GC specs. An important part of the cost savings idea with the Wii was for devs to be able to bring their last gen engines over.
A key point about those devs.....that really only includes Nintendo. Most of the GC devs who had worthwhile GC engines jumped ship once Nintendo announced wii wouldn't compete technologically, and so far most of the engine ports have been ports from Xbox or PS2. Nintendo didn't really have a large enough dev base to make engine portability important imo, besides Nintendo's own engine. PC based hardware would have been much more attractive for picking up where xbox left off.