I guarantee the smart defensive coaches (Giants, Rex Game 2, Broncos) saw this early on this season in the films (as early as Game 1) and told their guys hit him, you wont be called and there is a good chance he will.
IMO, in most of those OPIs, Gronk didnt initiate contact, he reacted to the defender. And in a couple it almost seemed like the defender play acted a greater push and may have initiated contact to draw the OPI.
Personally, i dont think they call OPI often enough, but just sad that they focus on TB's receivers and not Flaccos, Eli's, or Pay-me-a-ton's.