I think that if you're going to count, then you have to look at all major airlines worldwide. The aviation industry is seamless; there are major foreign flag carriers integrated into the US aviation system that to count only US-flag carriers is disingenuous to the discussion (IMO anyway). US citizens often find themselves on non-US flag carriers, especially if taking one of the vacation package deals to places like Acapulco, the Bahamas, etc.

Still, I agree with the premise that the aviation industry enjoys a relatively impressive safety record. I remember when US-Scare, uh, I mean, USAir, had a run of bad luck in the early 90s that it appeared to have at least one crash a year. I think that the FAA crackdown resulted in higher enforcement of safety standards as well as valuable lessons-learned from certain aviation accidents.

And, whether some in here like to admit it or not, I also believe that baggage screening contributes to the overall safety record as well. While the TSA mission is to screen checked luggage for explosives and incendiaries, TSOs incidentally come across a lot of HAZMAT in terms of flammables, corrosives, inhalants, etc. that serve as potential hazards which are turned over to the airlines and prevented from being loaded onto aircraft. Prior to 2002, there was no screening of checked luggage, and many of these items, while still prohibited, nonetheless made it aboard even when absent of malicious intent.

Then there's the other factor that can be anticipated but never truly prevented: human error. Pilots have to be perfect every time they fly. Every once in a while, though, in spite of all the systems checks and re-checks, human error will eventually creep into the equation with catastrophic results.

So I see this as mostly the result of new measures put in place coupled with better enforcement of long-standing safety standards with a dose of good luck.