We all know that a record doesn't tell you everything about a team, and looking at my week 17 ratings and rankings and comparing to who made the playoffs, this is evident on several levels.
First, Indianapolis is ranked #21 but is one of the 12 teams making the playoffs. This is due to 2 things, a very weak schedule based in part on having the worst record last year, and winning a lot of close games. Their performance chart is telling. You can see how their wins are mostly just above their rating while several of their losses are well below their rating.
But what about the teams that were "left out"?
Chicago is ranked #7 by my computer but lost the wildcard tie-breaker to Minnesota on division record. To be fair, my computer has Minnesota #8 just over 0.1 points behind, and Chicago is not ahead of any other non-division winner in the NFC. Their chart shows a clear decline in the second half of their year where they went 5-8, although all those losses were to playoff teams. Their rating is fairly high because of this tough schedule (#7) with only 3 playoff teams having a tougher schedule.
The Giants are ranked #10 by my computer but were a game out of the tie-breaker with Chicago and Minnesota. Had they won one more game, they would have had the conference record advantage over both of them and been in the playoffs. But losing 3 of their last 5 hurt them, although they too were to playoff teams. And losing early in the year to 3 teams that didn't make the playoffs didn't help.