Tyson admitted when he punched people he tryed to kill them. Others that unfortunately were on the dishing side of a lethal punch fell like S*** because they never meant for it to happen. Headbutts (accidental and intentional) happen more often than rabbit punches. Tyson only threw so many punches in his career but didn't kill anybody. The total of punches thrown without an intent to kill people far outweight the number of punches that tyson thru yet the punches that weren't meant to kill people killed more people than the ones that intended to.

Summary: headbutts happen more often so of course there's gonna be more instances to bring up the damage they did. Rabbit punches don't happen as often but that doesn't mean that they are in anyway equally or less harmful. The back of the head is a far more sensitive area where a lot of complications can occur. Complications that are way more serious than a headache, concussion, or, "god" forbid, a cut.