Just a rumor but here is the quote from
http://www.collegehumor.com/
-After 15 consecutive years of putting out games, the John Madden video game franchise is taking a year off. There will be no Madden NFL 2006. With EA Sports acquiring the exclusive NFL game license (and in effect knocking out virtually any competition) it will take an extra year off for research and development and completely revamp the game for a big re-release for 2007.