Maybe I'm being Captain Obvious with this crowd, but the 350 was ordered pre-merger to replace the 747, which was gonna fly until 2022. Post-merger, the 747 retirement got moved up considerably. First to 2018, then to 2017. So the 777-300s, which were available on short notice, are now the replacement for the 747. Evidently they tried to get out of the 350 orders, but could not (engines?). So now the 350s will replace our 777-200ERs. That's the way I see it.

Sled