At least CoD maintains this; there's still a good amount of people on BlOps and MW2. Now sports games? Correct me if I'm wrong, but don't they pretty much cut the servers for the old game? They also took out roster updates for the incoming year (when people would put out the upcoming year's rosters) from the download sections.
The advancements in sporting games haven't been enough to warrant a full new game; it's almost always graphic enhancement. They should restart the Madden and 2K series and just start from Madden 1 and NBA 2K I and update at a rate more similar to, say, Virtua Tennis so they're not required to "update" every year. This has led to rushed games anyway.