I have a hunch my casio wrist watch is designed to be running a bit too quick to make resetting the seconds easier. Your averaging assumes manufacturers try to make their watches as accurate as possible for average conditions

I think it runs quick to be on the safe side, so you never miss appointments, trains, etc. because of your watch.

But yes, good point.

This is the kind of thing that Casio designers would probably come up with (second to have as much accuracy as possible within their budget)

Given two time changes per year I guess something like 1 min per year is acceptable