I really don't think (or know how) EA is abusing the Madden franchise. You would be stupid to NOT release a Madden every year. And from a consumer standpoint, it seems logical to me to release a new football game every year. People complain that they're just releasing the same game every year, but it's FOOTBALL. The only areas I think EA can improve on are graphics and features, which they're done a reasonably good job on.
Anyways, I think only the most avid Madden fans buy the new version every year, while the rest of us renew every 3-4 years (which is what I do).