This is the league just being consistent. For example, in the investigation of the Jets tampering with Revis, the league took into account that the Jets had been accused of tampering with Deion Branch and Michael Crabtree and been warned about trying to tamper with DeSean Jackson. Or when Mike Tomlin stood on the edge of the field and prevented the Ravens kick returner from scoring a TD, the league took into account that the team had a recent rules violation for faking injuries.
Oh, wait. Neither of those thing happened. The league judged each of those cases in a vacuum.