Why is there no much fuss about the whole thing in Europe, where airlines strictly enforce low weight limits on carry ons? I've travelled on BA (which is definitely business oriented) often and they do so consistently.
I think it's just a matter of habit, rather than convenience etc. All of those who are "spoiled" into carrying huge carryons on board, or into not waiting 5 more minutes for checked luggage, would adapt fast into more reasonable carryon regulations. Such is human nature.