I know some people are complaining about this, but it is a sensible measure. After the volcano eruption in Iceland yesterday the high atmosphere is said to be full of volcanic ash. You can't see it, but apparently it will destroy an aeroplane engine. To me it is a sensible precaution, I think the people complaining would not like to be in flight and suddenly their plane turns into a rock! And the force of gravity is reminding the plane that it's heavier than air.
Here are some amazing pictures of the eruption. The force of nature at work there is awesome.