Thanks for posting this chart. Wow, what happened to the Wii in 2008? I wouldn't have even thought they would sell that much due to normal supply limitations.
Mario Kart Wii was released in April 2008.
Also, the supply situation for the Wii was intermittent. It actually steadily improved in sales from April to October of 2007 without any sort of price drop, which suggests steadily improving stock. Then in the Nov. '07 - Jan. '08 period, it wasn't really doing considerably better than the 360, with Q4 '07 having an abnormally low percentage of the year's sales, suggesting insufficient stock during the holidays. Then sales started to rapidly spike in Feb. 2008, with the Wii posting the best non-holiday sales of any home console ever in the U.S., selling a whopping 5.7 million units from Feb. to Oct. that year. The only thing that comes close to that was the PS2, which sold 4.52M in the Jan.-Oct. period of 2002.