Winning on the road in the NFL is one helluva task. I believe it is harder to win on the road in the NFL than any other league - and I'd even include the NCAA. The parity in the NFL probably explains most of the difficulty.
Just look at the first two weeks of the season.
Seattle goes on the road in Week 1 and barely beats Carolina 12-7, then comes home in Week 2 and destroys the 49ers, a Superbowl favorite and the team with one of the more impressive Week 1 victories.
The Saints look impressive in their home victory over a very good Atlanta team, and then squeeze by a dumpster fire Tampa Bay squad.
Congrats to Miami, San Diego, New Orleans, and Denver for pulling off a difficult feat this week.