I'll chime in here.
Players have said that in 2007, BB drove them harder than any year prior. Since then, some (Vrabel and Bru) have said that the emotional weight of being 18-0 was brutal and the team was a collective stress-case.
BBs psychology was to go Bear Bryant on them. Push them so hard and beat on them for every little thing (more than usual) that they really despised him, but also got them laser-focused on the tiniest of details.
So I don't think they were complacent at the end in 07. I think besides injuries and a Giants pass rush contributing to the loss, they were stressed out and emotionally exhausted. They were running on fumes and BB knew it.