zorg1000 on 03 December 2014
http://vgsales.wikia.com/wiki/Media_Create_sales_figures
According to this Gamecube was right around 3 million at the end of 2003 (it's second full year) while Wii U will likely be around 2.2-2.3 million by the end of this year.
One other thing to take note of is that GC launched in Sept while Wii U launched in Dec so GC has a couple extra months on it by the end of their 2nd full year.
When the herd loses its way, the shepard must kill the bull that leads them astray.
