I think these are simply cases of a very good team getting very lucky, and a very bad team being very unlucky.
When the Patiots went 16-0, they caught every team at the right time in regards to injuries, and all the breaks seemed to go their way, each and every week. That is until Tom Brady laughed at the Giants for predicting the score to be low.
The Lions were simply very bad due to poor management over the past 4000 years and that team simply seemed to quit.
Won't surprise me at all to see the Lions going 6-10/9-7 next year, all depending on coaching staff additions.
For the Patriots in 2009, won't surprise me to see them going anywhere from 9-7/13-3. Will be interesting to see how they do with McDaniels now gone. The Pioli move, if it makes a difference, won't be noticed for another year or so.