Thanks for all the details [MENTION=253987]flatlander[/MENTION] - as you can see in another thread, I've found a solution with STA: I need Qantas Lon -> Syd ->Mia, can I book return Lon/Syd and change booking in Syd?

I'm fascinated where all these tariff rules come from? I mean, it seems the concepts of the limitations here are not unique to a single airline?

Why would BA or Qantas effectively drive me away from doing directly business with them individually, only to then book the same flights with a 3rd party?