I thought it was Brees Overtime interception that cost them the game. 

PI is probably the biggest grey area in all of football.

*****

Agree.  It is called wildly differently in every game, and sometimes the same line judges and refs who were very liberal one week are incredibly conservative the next.  It's been said that if you look hard enough you can find offensive line holding on most passing downs but watching the games last weekend, it seemed like most passing plays had a reasonable case for flaggable PI (usually against the DBs, occasionally against the receivers; almost everybody is grabbing / hitting each other way beyond 5 yards and long before the ball arrives.)   I'm kind of glad they tend to allow the NFL players to win or lose the game on the field versus through ticky tack penalties (just like NBA refs tend to swallow their whistles on shots in the last 30 seconds of a game) but there's just no consistency and each ref seems to have their own criteria.