Sure there are are freak punches that do more damage than should.

Guys like Hagler/MArciano not only had god given talents to absorb punches, but also kept there chins tucked in, and crucially wouldn't panic as they knew that some big shots would get through, keeping composure so not to be vulnerable to the follow up which knocks your head off.

Guys like Hearns and Lewis have been mentioned over the last couple days, true they didn't have granite chins but they certainly weren't glass. Not everyone who isn't Hagler/Chuvalo/.. should immediately be classed in the same bracket with guys who get wobbled frequently by club fighters of a smaller weight class. Like Ono said, higher up the ranks the punches are naturally heavier regardless of records.