I sat through some school safety training this past year sponsored by the Indiana Dept. of Education, and a presenter, Lt. Col. Dave Grossman stated that many of the students at Virginia Tech. showed the same behavior, and they just sat there waiting to die and only one student showed any self preservation instincts at all, plus the one holocaust survivor who gave his life in their defense.
Perhaps it is the overabundance of video games in which death is simulated so graphically that they are numb to the fact that in life there is no reset button.
Lt. Col. Grossman also has a lot of good information on his website:
Killology Research Group: Lieutenant Colonel Dave Grossman, Author - Jonesboro, Arkansas Check out his press releases, they are quite interesting. Especially Bulletproofing the Mind: A Must for Concealed Carry.
(I'm new so I don't know if he has been referenced before, but his presentation for the Department of Ed. Safety Specialists was eye opening.)