If you are going to compare last gen in 2004 to now, you also gotta factor in that there were a lot more PS2's being sold compared to the number of 360's and PS3's being sold now. So yeah there's a lot of things to put into account instead of just "oh people are getting tired of Madden" .
While I'm pretty sure that EA wants Madden to do better I really wouldn't say that the game is in trouble at all. The game is still selling well. I remember reading just a few weeks ago that sales of the 360 and PS3 version were up 5% compared to Madden 09 for the 360/PS3 in the same time period.