The New York Times poured over logs from Madden NFL 11 games (human-controlled games by users with an Internet connection) and put together an interesting piece on the most popular teams in the game. According to the Times, more than 290 million games were started on Madden from Aug. 10 to Jan. 31, and the Eagles were used more than any other team in the league (likely because of Michael Vick; when he played for the Falcons they were a very popular team to use in Madden).
Looking at which teams were used and different trends for when teams' popularity jumped actually reveals quite a bit about how gamers react to actual events in the NFL. For the Vikings, for example, their popularity spiked after the arrival of Randy Moss and drastically dropped after he left Minnesota. The same thing happened with the Titans, whose popularity went up after Moss headed to Tennessee.
For the Detroit Lions, which overall were the 24th-most popular team in Madden 11, their use was pretty consistent throughout the season (see graph at right from the NYT). The only real jump appears to have happened after Halloween. The Lions beat the Redskins on Halloween and played the Jets a week later, and for a span of two weeks their popularity was higher than at any other point during the season.
With the Lions finishing the 2010 season on a four-game winning streak and having so many weapons on offense (who doesn't love throwing deep balls to Calvin Johnson all game?), I'd bet their popularity goes up a bit next August. How they play early on during the start of the regular season will likely have a big effect on their popularity, as that is the case for many teams. If they get off to a good start I'd expect their popularity to spike quite a bit.