Well in effect they are since EU and national courts are handing down judgements regarding the amount of noise being tollerated. It is a round about way. However if airlines cannot fly to certain important destinations with certain models because they do not conform - aircraft builders are more or less forced to come up with a solution or they will not sell their product.

It is a fact that europeans in particular the german courts are very pro indiviual rather than pro industry in this particular instance so airbus (bear in mind german interessts are fairly important here) is going about looking for solutions that will more than likely become an increasing factor in other countires around the world too.

Right now the aircraft builders are being given homework for the future by the airlines who in turn are facing the same development at many airports around the world.