While I agree with your logic, my experience with transcon flights on UA has been that if the flight number doesn't change (even though you are required to change airplanes), then it is only considered a single segment. (I doubt that your intercontinental situation would change anything.)

Personally, I think if a passenger has to change planes, the airline should be required to change the flight number. If the flight number changes, I know that I will have to change planes. But if the flight number does not change, I expect to stay on the same tube of metal all the way. To me, it is FALSE ADVERTISING for an airline to require a plane change while not changing the Flight Number.