That having been said, a blackout could be set up prior to a terrorist attack, and it would have the effect of magnifying the terror. Imagine the effect of 9-11 if New York's power had been cut just minutes prior to the attacks. As a force multiplier for a terrorist strike, it would be devastaing.
Also massive power outages would create holes in the radar coverage of the air traffic control system. Also, cell phones and possibly portions of the internet would go down. It's possible the calls to passengers on flight 93 might not have gotten through.
Rubbish ...