The Seahawks' success last season had something to do with role players emerging unexpectedly (Joe Jurevicius, Marquand Manuel, rookie Lofa Tatupu, etc). But as Mike Holmgren points out all the time, the Hawks's best players also enjoyed great seasons. Shaun Alexander and Walter Jones played better than they ever had. Matt Hasselbeck might have fallen into that category. Lots of other guys enjoyed the best seasons of their careers: Mack Strong, Bryce Fisher, Rocky Bernard, Jerramy Stevens and possibly Robbie Tobeck.
Now let's look at the current team. Who is playing his best? Julian Peterson and Josh Brown come to mind. Ken Hamlin and Marcus Trufant might be playing better than they have in recent seasons, but neither is a dominant player. Nobody on offense is having a great season. Darrell Jackson was putting up good numbers, but he is hurt (and he had also dropped a number of passes). When only two guys are enjoying great seasons, and one of them is the kicker, a team isn't going to excel.
The Seahawks managed to hang tough and win some close games while playing a weak schedule, but they have hit a wall more recently. An 11-5 record seemed almost guaranteed a few weeks ago. Now they might be fortunate to win nine games.