Check out this awesome scenario:
An NFL team plays in the toughest division. They go undefeated even though the games were low scoring. But, because 6 other teams play in crappy divisions they rack up more points and are awarded the 6 playoff spots even though they all managed to drop a game. Not only do they rank ahead of the undefeated team, the undefeated team doesn't even have a post season!
But as we all know that would never happen. Because that's dumb. Why bust your balls going undefeated????