At the end of the day the airlines have to decide whether they are in greater risk from suicidal pilots or from a terrorist action on the aircraft, its a difficult one to make a call on.
I also heard but not seen any confirmation that the French scrambled two Mirages to intercept the aircraft as it had failed to respond to ATC communications, lets hope that they did not play any part in this tradegy.
As far as the US system, earlier this year a pilot was locked out of the cockpit on a Delta Airlines flight, so that proves no system is fail proof.