Not surprised, when I go can to Heathrow - Edinburgh return with BA at virtually no notice, at reasonable times, for less money than it would cost me to go from Gatwick or Stansted with a budget airline. I get a comfy seat, I get something to eat, I get treated with a wee bit of respect / like a human, etc etc. I'm not counting the extra costsof trying to get to or park at Gatwick / Stansted - frankly Heathrow is easier for me anyway.
I've got no reason to be loyal to BA, other than any time I have flown with them I have had a good experience, and I've had pretty poor experiences with budgets. BA does seem to be good value for your budget traveller who wants a few extra frills, which I was surprised at - they've always been able to beat the prices of the other major airlines for me whenever I've gone out of the UK.