Let's not forget, these were kids, no adults. The kids had to face an automatic weapon, not an knife.
The brave people from flight 93 allready had knowledge of the intention of the hijackers and knew that if they didn't do anything they surely were going to die, where the people on the island had to hide untill the real police arrived.
XT, please give the source for your info, you seem to be much better informed than me. I am using Reuters:
http://www.reuters.com/article/2011/07/24/us-norway-idUSL6E7IN00C20110724 , which does not indicate use of any automatic weapons and states "mostly young people attending a summer camp", which makes me think there were adult victims, also.
If you see someone shooting everyone he can, that should be a pretty good indication of their intent. With that, you should know that if no one stops the shooter, more will be shot... more will die.
If you think you have to run and hide because someone starts killing folks, you are not helping to end the problem. I understand it, you want to save yourself and you might want to get family or friends to safety, you are fearful about the outcome, but if you give up taking an active part in your security because you believe someone not at the scene can help you in an active shooter scenario, well, may others learn from your mistakes.