The single biggest difference is the play of the respective quarterbacks. Both defenses have been, on the whole, very bad. Both offenses have been, on the whole, very good.
Offense:
NE:
- pts: #4 (27.8/g)
- yds: #2 (437.3/g)
- SRS*: 4.8
- giveaways: 14
GB:
- pts: #1 (34.4/g)
- yds: #4 (416.4/g)
- SRS: 11.9
- giveaways: 8
Defense:
NE:
- pts: #20 (23.0/g)
- yds: #32 (416.3/g)
- SRS: 0.0
- takeaways: 14
GB:
- pts: #17 (22.4/g)
- yds: #30 (399.6/g)
- SRS: 1.2
- takeaways: 19
*SRS is the simple rating system devised by profootball-reference.com
So the turnover aspect of the equation is really the difference maker. GB is +11, while NE is even. If each turnover is "worth" roughly 4 points (from another thread), then that's a 44-point difference between NE and GB. And 44 points through 8 games = 5.5 points a game. That's plenty enough to make up the difference of 3 games.