Quentin,
Unfortunately you have made some invalid assumptions in your post. I don't fly this sector so I'm having to make some assumptions as well, and I'd appreciate those who know correcting, however:
- The 747ER can't fly chock-full of people and freight DFW-BNE. They fill it up with fuel, but they have a restricted takeoff weight simply to make the distance - it may well be that they can only take 300 pax + a small amount of freight (if any).
- The A380 will probably take 380 pax or so from DFW - SYD, maybe a bit more or less depending on the time of year and depart at MTOW. The seats that would be blocked off would be economy, and there would be a far greater number of premium seats being sold on the A380 than the 747. ( If we are doing like-for-like, certainly I'd say it would do 450 - 480 pax from DFW-BNE. )
- It looks very much like this is to link in with Emirates, so they need First Class and the upgraded Business class for this service.
Whilst the details of the figures may be a bit rubbery, I think you get the general picture. Of course it is possible the 747 can take a bit more to BNE, however it has no First Class and would not enable the link-up.
N