The question, surely, is how the authorities define an "ash cloud"?
Up until now all procedures and rules have been based on the sort of cloud that one can see and avoid. The 100 (or so) airliners that are quoted as having encountered ash clouds since the 70s were flying in a big, black mass of ash and rocks - easy to define and one knows that one flew though it.
How can they tell us that we must avoid invisible clouds on pain of death and destruction without also mandating that we never leave the ground?
More interesting to me (because I didn't stop flying) is the behaviour of those making the rules. Why did they not (quickly) ask people who have done this before? Alaskan Airlines have rules and procedures for volcanic eruptions because they meet them quite often. Iceland has had eruptions before now and managed without bringing the continent to a standstill.
Our European regulators and politicians seem to have sat tight on their overfed backsides until the industry shouted loudly enough to make it very uncomfortable. I'd like to know why they weren't doing the job they are paid to perform on our behalf?