BA is traditionally a Boeing only company, but with Virgin, Singapore Airlines and others flying A380s out of Heathrow, and given the shortage of slots in Heathrow, not flying the A380 will put BA at a severe disadvantage on it's home turf. BA isn't in a good financial state at the moment, so it will delay buying as long as it can, but I believe it will have to come round eventually.

As for the A350 being a new aircraft, it kind of makes sense. Announce it as a 330 variant to try to stall 787 purchase decisions (the same as Boeing did for the 747 variants to compete with the A380) and then launch an all new plane to compete in a different range (just like Boeing did with the 787)? I wonder if the A350 will be launched to compete with the 777 rather than the 787. It would kind of make sense to do so since the 777 is less modern than the 787 and so the A350 will have a more compelling market there.