I don't think they are so much falling off in NA as adapting to the fact that the Wii is now in supply at most retailers.
On the spot purchases due to availability are going to disappear.( there is no need to rush and purchase the Wii you see on the shelves now and people will delay their purchase ( especially when offering it as a gift)).
PS : I think his comment was related to the fact that last week NA wii sales were the lowest weekly wii sales since the stock issues of early january.








