my guess is that those flights (735 and 754 for the 2 flights I remember on top of my head because I've flown on them) are meant to be "direct" flights with a refueling stop.
But due to the post 9/11 procedures, there is now a requirement to clear customs and immigration at the port of entry.
So it's probably more cost efficient for US Airways to have a 757 do the second leg instead of refueling an A330 for just a short hop down to MCO, since all passengers have to get off the plane and reboard.
I also remember a "fake direct" flight with United, CDG-EWR-MCO that bore the same flight number, and United broke that flight into 2 seperate flights a couple of months before our departure (which led to a nightmare with the TA who refused to understand that the EWR-MCO leg no longer existed, when in fact it was the same plane but under another flight number ... took me weeks to have them change my tickets ...)
I try to see those flights as a train, like Eurostar for example.
If you take the train in London, it still has the same number wether you get off in Lille or in Paris. There is not a different train number between each train station
well, I guess it doesn't matter anyway
