Tripower,
To answer your question to me. The reason why it increases the likelyhood of a dead pilot is because the terrorist knows you may well have a gun in the cockpit therefore he will have to act much more quickly to incapacitate you. Previously he could just threaten you with a knife. Now the stakes have been raised. He knows he must get you before you get him.
Furthermore not all pilots or cockpits will carry guns. However the terrorist has to assume that there is one in the cockpit, as there is now the possibility of there being one. Therefore the terrorist will now be much more aggressive in his approach, with little chance of the pilots defending themselves, even when no gun is actually present.