The Xbox costs more and has more goodies inside, but the Gamecube sold more units with weaker components inside, fewer games at launch, and with fewer marketing dollars backing it up. The Gamecube's lower price and key franchises creates competition, which Microsoft will need to get used to.
I think this next technology war, the console war, will be a long and bitter fight, which is exactly what I want to see. The competative advantages of the Xbox vs the Gamecube are equally strong in both directions. If it were all in one console, the PS2 would simply not matter (and perhaps it doesn't right now to lots of Linux geeks). The longer it all goes on, the more the competition will provide the usual yields that competition brings.