I'm going to post what no one seems to have mentioned - the airlines were in trouble, deep trouble, even before some terrorists dialed 911 on the World Trade Center. But no one wanted to be first in slashing schedules and workforce, for fear that others would crowd in and take business.
The attacks provided the cover for the airlines to layoff and slash in unison, fairly secure in the knowledge that the others would as well. I wouldn't be surprised if there were some *wink* *nudge* communications about it - but it isn't necessary that there were.
The basic truth is that we are in recession, we have been in recession since June or July. The fast paced internet economy flew people around willy nilly - I knew people who lived in Boston, but were commuting to New York on the Shuttle at customer expense - that's right 200 dollars a day (buying at advanced prices with a corporate discount) every day they had to work. That isn't happening now. We may be flying as many miles - but the over all budgets for flying have plummted. Business trips are now planned well in advance, and saturday stays required on airlines that haven't lifted the Saturday window for whatever reason.