These figures are based on polls and other sources I would imagine. Mostly speculation. In my humble opinion, this means nothing. They are predicting the future, but without a clear full view of it. Who knows what killer titles could come out for the Xbox bewteen a 4-5 year life span? The same applies to the GameCube.
I do figure that the GC will outsell the Xbox at launch, but that is simply because of brand name and franchises. Nintendo can sell on that alone, where as MS has alot to prove to the industry. But, I refuse to predict any further then that.
Ignore these so called "news articles". They don\'t have a crystal ball that tells every game and every marketing type that will come out within these next few years, so they know nothing.