Then technically the XBox is a failure as well. It's only leading the GCN by 900,000 units worldwide. That's less than the population of Idaho. Also, take into consideration that Nintendo has been making a profit on all hardware and software sales since the launch. Microsoft has been losing money on hardware sales since the XBox launched.
The Gamecube is hardly a failure. It's just not the freakish monstrosity of a success that the PS2 is.