£100 one way. Take £13 for apd (you pay it both ways for domestics!) plus gatwick charges I would guess will be about £20+ a passenger and handling will be more expensive. Plus I doubt they were achieving an average of £100 each way on gatwick, v v v unlikely!
Corfu will sell 90%+ of seats at upwards of £100 avg one way.
Gatwick loads where in the 60-70% ish and I reckon average fares around £60-£70 minus £30 ishin charges and tax.
Once the aircraft is cruising it's not burning huge amounts of fuel and crew is paid for, plus long flight lots of ancillary revenue from the holiday makers drinking lots, eating lots and buying lots of tax free ...
I'd say more money to be made on Corfu, but like you I don't have access to figures, just thinking aloud ...