Groundhand:
"Can you imagine trying to staff, provide ground equipment etc. with no guarantee of revenue?" You mean like the airport operator has to build and run a whole airport with no guarantee of revenue? Handlers can lease equipment on a contract that they can terminate at any time, and of course they can sack staff if there's no work. Airports can't give their bricks and concrete back to Jewson and get a refund, can they?
"Some of the floor space in UK airports is at the top of the retail rental market, never mind the turnover % that is raked off as well." I think you'll find that shop and services concession fees are based on turnover, with a minimum fee, and offices/ramp space etc. are usually flat-rate rented. I doubt any service partner pays rent and a concession fee.