Between the UK arrests and the above post terrorists have already killed civilians on the ground; and those attacks had nothing to do with bringing down an airline. So much for the theory that "the terrorists would much rather bring down an airliner". That is, the above timeline implicit in the post above is not correct; it leaves out a whole stream of terrorist attacks that have happened between "the Madrid and London subway bombings" and "the latest plot" involving OBL & Co writ so very large. And nearly all of those had nothing to do with air travel.

The impact of terrorism can also be measured by the government and societal responses that follow an attack or a bust-up. By such measure, even the absence of an executed attack this time has greater impact than the London and Madrid attacks noted above. However, it is clear that more people were killed in the London and Madrid bombings than in this plot. Does that mean that there was less impact or more impact from this plot than those bombings?

It's clear to those that actually look at hard data in this area that air travel is the part of commercial passenger transportation that is far less frequently hit by terrorists than other modes. Of course that fact doesn't sell well to the stirred-up paranoid crowd or to the neo-PC crowd that says "don't harass me, harass 'them'; I don't look like a terrorist, 'they' do, so go after them".