Football Outsiders does a good job at incorporating other stats and factors into their analyses that most other places ignore, but their rankings are still based on stats from the games. So what someone mentioned earlier about how other teams have run more on Detroit than pass would still skew FO's rankings a bit.
Bly is a decent corner, but nowhere near the talent some people are suggesting after looking at his numbers. And Bly's numbers may have been a bit inflated because Detroit's other corner is complete garbage, ranking 32nd against #2 WRs (according to FO). Granted they've been stung with injuries to Fernando Bryant, but he sucks regardless.
Teams at the lower end of the NFL always have inflated pass defense rankings because they are losing so often, opposing teams mostly ran on them. Happens all the time and lots of people get taken in by that.
PS: OMG, BH made a comment where I can't detect his normal biting sarcasm...
But then he comes back with the "Inside" comment so back to normal, eh?