I think the bigger difference between the first 3 games and the last 3 have been injuries, offense and back-ups...
First couple of weeks, Burnett was injured and the DBs struggled big time especially the S positions which have calm down since.
The Redskins struggled but Packers defense seem to relax on them since the offense got so far ahead.
I thought the Packers defense played well against the Bengals, other than the first drive and a small handful of big plays, the offense just kept giving the Bengals more chances.
Yes the Packers have gotten injuries but the Lions were missing Calvin Johnson and their other starting WR. And lets be honest, when fully healthy teams have to game plan around Johnson.
The Browns had their best QB injured for the year and haven't done too much since and honestly I think the Packers could of put that one away early but after the first two or three drives the offense seemed to get comfortable and the OL didn't seem to stay as low or have as good of pass rush after that.
And yes while the LB have been banged up and injured lately, between the back-ups stepping up and Capers using some adjustment tricks such as blitzing different guys ( ILB / DBs) more often they're been able to help step up for those areas. Where if the Safeties are playing poorly, there are very few tricks you can use to help them out, because like CBs they're kind of out there on their own at times.