The Madden guys are obviously putting a lot of stock into the free agency additions/losses.
I guess from an outsider's standpoint, the losses of Smoot and Pierce would presumably have a devastating effect on the Skins' defense (or at least their Madden equivalent), especially when the D-line wasn't upgraded at all.
On the other hand, the Vikings and Chiefs made several splashy free agency additions to their defenses, so you would expect their ratings to go up...
Personally, I've been modifying the league rosters on Madden 2005 ever since free agency started, creating draftees, and altering the players' attributes to more accurately reflect (at least in my mind) the players' real-life abilities. I think my version of the Skins' defense will be rated a little bit higher than 74.
I always like to do that in the offseason to see how my projected team and player ratings compare to the ratings in the new game when it comes out. Yeah, I know, it's totally geeky-- but I get pretty damned bored in the offseason.