I can see your point where the big BAA airports are concerned, infact anybody who can afford to use NATS can't be short of a few quid. However, spare a thought for the smaller outfits who are trying to turn a penny in todays environment. The cost of running an airport whilst addressing the many external influences (SES requirements, wind farm applications, environmental pressure etc etc ) gets steeper every year. Add to this the move towards paying Low Cost operators to use you airport and you can understand why so many have to take revenue where they can get it.
I sympathise with the point, but while it's fine to refer to overseas airports let's remember that they also have their own little revenue earners (Airport Development Fee anybody?)