Well I live (approx.) midway between Heathrow and Birmingham and closer to BHX than to LGW. However, I never fly from BHX for a hatful of reasons (most of which are observations, not the results of systematic enquiry)... low cost tickets seem to be more expensive from BHX than from London. Flights to Europe tend to be less convenient and less frequent from BHX. My transatlantic airline does not fly in to BHX. I am not crazy and therefore would not fly Transatlantic in a 757. If things get screwed up in London, I have a better chance of getting on another flight. Habit.