I can't imagine it does that much to remedy a poor-fitting hang.
On the other hand, wouldn't figure it does much of anything to the integrity of the head itself.
Here is a pulaski I picked up with the same "pin hole". It's really clean like it was done with a machine and maybe not by the end user.
Probably what 300six was saying. Extra safety insurance - "insurance" being the operative word.
Personally, not a fan of the pinning hole solely for cosmetic reasons. I have two pickaroons and they both have the holes - one with the pin still intact. On the pickaroons, my assumption was that it was because you are pulling the tool as much, if not more, than applying lateral force like with an axe. There is also a lot less material in contact with the handle. Maybe someone thought along those lines with the Hudson Bay?
Might have been something common in an area or during a stint of years where "safety/liability" was of high priority. Maybe some were ordered that way?
Wondered the same thing but these are guesses. The hole wouldn't stop me from picking up a user though.