To further expand on my point...
Divisions aren't arbitrary; geographically based divisions reduce travel time and expenses, foster rivalries and uphold tradition, and create better scheduling structure.
For a team to not make the playoffs in the NFL, they have to place behind at least three other teams in their conference. For a team to finish second in their division and still miss the playoffs, they have to place behind at least four other teams in their conference. As it is, the Patriots finished behind five teams in their conference. Woe is this sixth best team in a conference when they fail to make a playoffs.
The rules are the same for everybody, and that's why it's fair. The six teams with the best record in a given conference won't always make it. In fact, they usually won't all make it. Still, instead of creating a sixteen team conference pool (which nobody does, why do you think?) with inevitably uneven schedules, you pit four teams against one another, give them virtually the same schedule, and guarantee the winner with a playoff spot. Then you do the same thing with three other pools of four. You don't know which pool of four will be good and which will be bad in a given year, but that's why you have two, count them two, wild cards for those teams that excel while being stuck in a division with other excellent team(s).
Maybe the fifth best team will be left out, maybe the sixth best team will be left out, but who gives a ****? Who gives a **** when Florida State or Creighton or West Virginia is left out of the NCAA tourney when Valpo and Deleware State make it in... besides FSU, Creighton and WVU fans, of course?
The NFL is about more than the playoffs. It's why we have a regular season! Divisions matter. Rivalries matter. Geography matters.