Well I don't live IN Sipson but I know the area well and it's a little island of nice houses sandwiched by an airport and some less than salubrious areas. I'm not unfamiliar with the issues....
Your point on connections works for Manchester but the forced train opton will make connecting passengers use KLM / Lufthansa / Air France and consequently see fewer jobs at Heathrow as the feed bleeds off abroad. It's much quicker to connect over KLM ex MAN / AMS than get the train to Heathrow and connect to BA or another British carrier.
What about GLA / EDI / NCL etc? They'll just connect abroad and STAR and BA will have no feed for their Heathrow long haul services and focus more of their operations abroad. I'm very concerned that people are very keen to play the green card on the day the UK is officially in recession.