I ran into this on the Daily Norseman and thought it was pretty interesting. An article from the NY Times goes over the popularity of the 32 teams over the course of the season and notes reasons for spikes and declines.
Throughout the course of the season, the Philadelphia Eagles were BY FAR the most popular team on Madden. It was clearly the doing of one Michael Vick as his emergence on the scene sparked a fast climb that really never went down. The Minnesota Vikings coming off their great 2009/10 season were the #2 most popular team though it fell quickly with the departure of Moss and the decline of the team. It shouldn't be surprising with how they did last year that they were a popular team. The Baltimore Ravens slipped into the third spot and were amazingly consistent throughout the year.
The Packers finished the season on the top as the most the popular team after seeing a very steady climb once the playoffs hit. After beating the Bears they rose to the top and it wouldn't be surprising to see them in the running with Philly and a few other teams for that spot at the beginning of next year (as long as Vick stays in Philly).
The Cardinals sat in the basement for most of the year with almost no movement the entire year. A few shockers though were successful teams like Tampa Bay finishing at #29 and Houston Texans at #23. To some, seeing Oakland in the top 10 might be a shocker but speed kills in Madden and we ALL know how much Al Davis likes speed with his players.