Erm, is it just me or is the Wii not behind the PS2 in that graph the OP posted? :p
And bear in mind that the Wii demand had been bigger than supply inch launch, and that the Wii hasn't seen any pricecuts, new models, bundles or alternate colours yet at all. The Japanese are crazy about new colours. :p
Nintendo Network ID: Cheebee 3DS Code: 2320 - 6113 - 9046