I can agree with this mainly because of free agency and the money players now make compared to earlier eras. Teams love to pick off free agents from play-off teams these days. The Patriots didn't even win the Super Bowl and they lost some big names from their team. The money and length of rookie contracts seem to play a big role these days: get for about 4 years and then lose the player after 1 or 2 great seasons thus keeping a good core of players much harder.