I can see both sides... On one hand, it's nice to not have teams under .500 make the playoffs often. If you don't win as much or more than you lose, then you shouldn't be in consideration for the championship. The Eastern Conference in the NBA this year is going to have multiple sub-.500 teams make the playoffs this year. Don't want the NFL being like that.
At the same time, the NFL has more franchises than the other three major sports, and only baseball allows fewer teams into the playoffs, with 10 total. 38% of NFL teams will make the playoffs... 35% in baseball, and more than 50% in NBA and NHL. I think you could stand to add one team in each league, which has been discussed. The AFC's last playoff team was 9-7, and everyone that was left out was 8-8 or worse, but Arizona got left out in the NFC with 10 wins. You win 10 games, you should be in.