Sad and unjust
BAA is effectively a monopoly, and it certainly acts with all the arrogance of a monopoly.
It is cross-subsidizing the development of STN with profits earned at LHR and LGW. Their only London-area competitor is Luton, which is far smaller and has been short-changed by decades of Local Authority mis-management. They find it easy to rubbish Luton, and can give the world's airlines a 'choice' of three London area airports.
Whilst aviation-related charges are capped, the money that BAA can earn from concessions and property rental is unlimited, and with the increase in property values combined with air traffic growth, they win both ways. TBI on the other hand is a small company with comparatively few resources.
The only solution to this situation is for BAA to be broken up, with London airports split into 2 or three unrelated companies, and perhaps a division of EDI and GLA (which are probably operated to the detriment of Prestwick).
The Government had their opportunity to do this last year in their Whit Paper, but failed. I'm afraid Luton will remain the poor relation unless airlines at LHR/LGW start to object to BAA cross-subsidizing their competitors at STN.