Originally Posted by
ethernal
Somewhat off topic but does anyone know the logic behind this policy? That is one thing I love about United (oops, need to fly out of LHR a couple of hours later? No problemo).
It's not logic, it's the business plan.
AA does not permit SDC on international for other than JFK-LHR and that is a route with multiple daily services and AA charges $150 for that (other than for its top level elites). Non-US carriers generally don't permit SDC other than for fares just below full flex, so it's really just UA.
Bottom line is that DL is very protective of its premium brand and high-end fares. It charges a fortune for flexibility on international routes and there is no reason to undercut those fares.