I wouldn't go to Newcastle to fly to London, by the time you have faced the western bypass, you could be halfway there by car.
It would make sense to go to the USA via Dublin, IF the flights were timed to connect and IF there were sensible fares.
The link through AMS allows KLM to do consolidated fares which mean business class flights for around £2k, rather than the £5k through Heathrow.
Don't think there are any cheap flights from DUB. Maybe an opportunity for someone like Eos?