Y'know, the object of terrorism and the desire of terrorists is to instill terror. To that end, the threat will suffice. It throws people into a tizzy, daily routines into confusion, and causes expenditures of manpower and money. When the attack doesn't materialize, well, there we go, crying wolf again. The terrorists just go to ground until the security slacks off.
However, the object of a brainwashed terrorist is to kill americans. While OBL et al may just want to "instill terror" theyve brainwashed the lower level op's, they wouldnt care if they disrupt our "daily routine"
The Koran doesn't say anything about instilling terror or disrupting our lifestyle. The goal is to end our society by killing or converting us.
Though I do agree, there is strategic value in crying wolf.