Couple of things effecting this.
1. Only the hardcore get a new madden each year. I used to only pick up madden every couple of years. Now with my 13 year old son he asks for madden each year as a birthday present. Since the Wii demographic for the most part is very casual less people will get a new madden each year.
2. As this generation progresses more people will have both a Wii and a HD console. If your one of those people you will get the HD version of Madden.
3. A large amount of people getting a Wii are getting it for a specific game or 2. For instance I finally succumbed and picked one up for my wife for Christmas with WiiFit. Neither I nor my kids have little interest in other games for the Wii. The Wii will go in my bedroom where my wife can work out and the 360 stays on the plasma in the family room.
Its libraries that sell systems not a single game.
