I think the issue is when the Patriots win the Offense generally overcomes the shortcomings of the Defense. However, that is flipped in a loss and the shortcomings on D generally always show themselves during a loss, something the Offense cannot overcome if they play poorly.
I happen to think the Patriots outsmarted themselves this weekend and refused to make the proper in game adjustments against the Steelers. The coaches were adamant Mike Wallace wouldn't beat the Patriots over the top so the Steelers took what was afforded to them. Amongst all that and a pitiful New England performance, they still had a chance to win on the last possession against a good team in a hostile environment.
As I've mentioned before, the Patriots are still in the elite category of teams but all are seriously flawed this year. The Packers appear to be the least flawed of the lot, but they've got a potential HOF QB pulling the strings playing career football.