I can see your point. But i can't really agree. The reason you see some leftkick knockouts is simply that it's most common to circle to the left. Against vicious bodykicker's like Pettis or Machida you're just going to get wrecked if it hits you clean in the liver, which is why you should be blocking it.
If you circle into the bodykick, you create a collision. Big homie Jack Dempsey put it best in Championship Fighting, if you drop a little baby from a tall building onto the head of a big tough bruisher, tough guy is getting knocked the F out, at the least. (A little graphic, but it does the job).. Baby can't hit him hard, but the collision is created = the damage is bigger. A frontal collision between cars would be way worse than if only one of the cars was in motion.
Machida is a master at this -> Tito moves into the knee strike = impact is doubled. Same thing with Bader. Same concept when circling into a kick.
Also, boxing trainer's necessarily adhere to a strict "circle away from the powerhand" mantra.. I mean it's kind of common wisdom or whatever, but a lot change it up, especially to inside slip and get on the inside.
I commend you for seeing the pattern though, individual thoughts are a rarity around here these days.