I prefer to think that they lost because of sub-par talent at key positions, lack of locker room leadership, and mental toughness. It's a combination of all three on top of some uncharacteristic boneheaded decisions by the coaching staff. I expect the 2010 team to be better.
Against the good clubs the 2009 Defense was unable to get off the field. Yielding 110 yards per game and 4.4 YPC is enough to lead to a losing record. But the Pats were too good for that on Offense. The 2002 Club would have had a losing record. And the Rush Defense was only mediocre but not atrocious.
None the less, Belichick treated that weakness as something so important that it warranted fixing over all else. Anti-run CB, anti-run SILB, anti-run DE--> OLB; and signing two former First Round DLs to patch the hole Seymour left. I've never seen Belichick spend so much effort on a single problem.
Nevertheless this Defense is much better than last season's edition. Leaving the opposition in 3rd and 6 will automatically give a much better Pass Rush and pass coverage too, than constantly facing 3rd and 2.
This Team's Offense is still not decayed enough, to not be a total terror. The Offensive line is talented and very, very, deep. Imagine this WR corps in the latter part of the season. Two future HOF WRs and a All Pro slot receiver, to go with a very good TE and H-back. And then add in Faulk, or go 4 wide with Tate. That would give every DC heartburn. Plus you can't just forget about the run.
The RBBC should produce just as well this season, as last. Nothing spectacular but lots of yards piled up on the ground. I would not want to meet this Team in the Playoffs, after the Team has a chance to jell.
The only weakness I can see, is whether Brian Hoyer is ready or capable of doing a good Matt Cassel imitation, if needed. I suspect he is not ready for another year. I wonder if Belichick will sign a vet QB?