Steyn is right. I will bet that a large number of them thought that the police would be there any minute to get this guy -- and they never came.
The thing that plays into this, I think is something that the military has always been aware of , but you rarely here it spoken of amongst civilians. A soldier (and similarly, a citizen), when faced with overwhelming violence, has to be taught to defend himself. It is rare to find an individual who instinctively strikes back. Especially if he is in a crowd, the individual watching violence approach instinctively freezes , and assumes a posture least likely to call attention to itself. It is the instinct of prey, and it happens so often on the battlefield amongst undertrained and underled troops that it is a truism.
Sentient reporters would recognize this as the behavior of the bystanders at that mall, and in seeking to understand it and explain it, would go a long way toward teaching us something about human nature.