That graph really isn't fair.
Ps2 was in Japan only for a while, while they added up more stock.
A more fair comparison, would be Ps2 in the same time of the year and out as Wii.
Wii sales - week ending 25th November 06 to end of Q2 07: 8.89M
Ps2 sales - week ending 28 October 00 to end of Q2 01: 7.73M
So considering Ps2 has 1 month more above, you can say Wii is selling 20% faster for the first 8 months.
Over the next year, Ps2 sold 18.2M
Wii sold 20.5M
So the Wii is steadily selling ~ 10% more than Ps2 was in the same time frame (not ~ 30% as the graph in the OP suggests).
http://www.vgchartz.com/games/userreviewdisp.php?id=261
That is VGChartz LONGEST review. And it's NOT Cute Kitten DS







