In case it wasn't abundantly obvious, the "brave" part that I wrote was completely sarcastic. There was nothing brave they did that day. Personally I doubt there's anything brave any of those guys ever did in their entire lives.
But these are people who are at least accustomed to being in a job with an above average level of danger from other people. They're armed, trained and at least in theory: prepared for hostile people and have accepted their role to protect. The average American riding on a 737 is none of these things. It's just a random Joe or Sally with a ticket for a weekend getaway. To believe that they would, on average, outperform in the face of dangerous, harmful people is wishful thinking IMHO.
I stand by the notion that the overwhelming majority of people would sit idle and hope the person next to them acts. I know on a plane it's different than the school situation because everyone's in it together and the religious fundamentalists have proven they like to take everyone down with them... but I still believe humans are exceptional at abdicating responsibility and waiting for someone else to step up.
You see this behavior outside of airplane hijackings, too. You can look at many mass atrocities that have been committed where victims greatly outnumbered the perpetrators. Rather than revolting and avoiding a certain death, many just did what they were told and waited for the inevitable. And so the inevitable occurred. Brave people are always in shorter supply than you think.