Quick post, but I wanted to show you all that I'm not daff. Jim Armstrong at Football Outsiders keeps a drive stats table sorted in a lot of interesting ways. Here are the Hawks performances in two very important categories during the John Marshall era (2005-2007).
2005
Yards Per Drive: 27.07 (15)
Points Per Drive: 1.44 (7)
2006
Yards Per Drive: 26.84 (12)
Points Per Drive: 1.66 (15)
2007
Yards Per Drive: 30.43 (22)
Points Per Drive: 0.61 (6)
You'll notice that they allowed the least yards, but the most points in 2006. It's also the only season that Seattle's points per drive ranking didn't greatly exceed their yards per drive ranking. I imagine the loss of Marcus Tubbs, the nagging injuries of Rocky Bernard and the decline of Grant Wistrom kept Marshall from implementing his attacking, bend but don't break defense. Anyway, the larger point is that yards allowed does not equal points allowed. So, yes, T.J. Houshmandzadeh and Chad Johnson combined for 279 yards receiving, but Seattle limited the dynamic Bengals offense to just 21 points.
Again, the Seahawks have a good defense. Yards allowed is not a good indicator of a team's defense. Please stop citing yards allowed as conclusive evidence of Seattle's defensive performance.