Soooooooo, the one time it happened means it always happens? Oh come on! Really? They can see on their computers at the gate where connecting pax are, and if they have a good chance on making it. If they do, they wait. That's why as a Nonrev you do wait by the gate. If those connecting pax don't make it, they can still fill all the seats. There are mitigating circumstances for some planes to leave ontime or near it, maybe slot times or quick turns coming back, headwinds, whatever. (going across the pond isn't the same as being the last flight of the night to Amarillo). Sounds like the duty manager made a DECISION, and stuck with it. He gave them 20 mins too. He tried. That is customer service.
Bye Bye---General Lee