Shed I agree with you, and if I were in Manchester I would not choose to fly all that way with two stops rather than one. However, airlines are not uniform bodies, companies can be quite competitive internally and the business case for the A380 and the SQUILLIONS of dollars that was spent on the hardware was to get as many peeps as possible on board QANTAS with good seat mile costs.
Jetstar was partially created to retain the QANTAS presence in markets they were unable to be competitive, this collides full on with the introduction of the A380 into London as this was bought to ensure QANTAS remains competitive in delivering armies of Aussies to it's Oneworld partners at the European end to connect onto their final destinations.
It's not that long ago that BA were booking people over LHR-JFK rather than the direct MAN-JFK service as it can depend on "whose" passengers they are within a company. It's barmy but it's true. MAN is better off with Emirates, Etihad and Qatar, but I feel many still pine for the old legacy days of the old flag carriers and will never admit it. Now that's also barmy but I do understand it.