I can understand the regulations but at the same time it sure seems crazy for that to be the policy for checking a carry-on at the gate. There's no change in total weight when a bag that was intended as a carry-on get checked.

It makes you wonder the affect on the calculated average weight of passengers when things happen that change the general population's baggage checking habits, e.g. TSA prohibiting liquids in carry-ons, or airlines charging to check a bag. Do they account for these things?