There is a difference between the GATE and the TICKET COUNTER. The ticket counter is where you get your boarding pass (if you didn't print it at home) and check your luggage and is where you find scales. The GATE is where you board the airplane and they have bag sizers to see if what you want to carry on will fit.
In the US, the only place I have ever seen a scale at the gate was the Air Canada gate at the Denver airport. They were sneaky about it too because they had the scale actually on the jet way half way to the plane. They both measured and weighed my carry on last summer when I flew to Toronto. Lots of people were complaining about it not being fair that they were being forced to check their carry ons (mine was OK). I have not had my carry on bag weighed at the gate anywhere else in the world so far.
Many airlines have weighed my carry on at the ticket counters. Lufthansa from Denver is the wurst about that. Even though I can print my boarding pass at home, it states I must check in at the ticket counter before going through security. They always insist I place my carry on on the scale. I have not had that issue when flying US based airlines internationally, but within Europe it seems every airline wants to weigh my carry on at the ticket counter.