Well let's say it's both. While I agree with you that Madden got off to a rocky start when they rushed to deliver Madden 06 on a short cycle, they also had to make much higher payments to the NFL that same year which I believe cut into the development funds.
Also as people often point out, this game is not developed on 1 "engine". Every year they choose which ones of the multiple "engines" to rip out and redo. By the 5th development cycle (Madden 11) there should be almost no trace of the slapped together abomination that was Madden 06 code.
Some more reasons I believe my theory to be true:
1.
EA now typically spends two or three times as much on marketing and advertising as it does on developing a game. A game like Madden has no comparable game like it and no alternative football game. This is simply funds that are being denied to the development team.
2.EA is a company that is unstable financially. I don't believe they see a benefit to dumping large amounts of money into Madden development. Football fans will purchase even if the game is subpar. A more practical approach is to get the gamers to pay additional funds for things like Madden moments and AFL packs. What EA is really out to do is increase the amount of casual gamers. They make the game quicker, simpler and more arcade to try to achieve that goal.
3. People always point out, the Madden series is improving but just not fast enough and lags behind the Show and NBA2k. Could it be that those games just have more funds for their developers to work with?
4.Ever noticed how the game improvements always seem half baked? For instance, they add Gus Johnson but he sounds broken and Chris calls him "Tom". Ian himself came on after 11 dropped and said they needed new equipment but spent the money for the sound budget securing the rights to the stadium songs we hear in Madden 11 instead. This tells me there are times when Ian is being shortchanged in his attempts to improve the game.
5.Those same stadium sounds were held out of Madden 10. Again, I don't believe this is Ian's fault. I think EA made a poor decision and chose to deny those things to us because they felt they already had enough improvments to sell Madden 10.
These types of business moves will tie the hands of any designer whether it is David Ortiz, Ian Cummings or some new replacement. That's why I don't believe Madden will see a major change if Ian leaves.
Sorry for the long post. If you got this far, thanks for reading.