Michael SWS,
I agree with you that the total cost of getting from A to B needs to be considered. Getting to Heathrow may cost you £2 but for others it's considerably more. And what about those who can't stand the ghastly experience of travelling to LHR by tube? If you factor in the price of travelling by Heathrow Express or even Heathrow Connect the sums look different.
At the moment, for me BA is never cheaper, but then again Stansted is my local airport.