I think a lot of people don't give the upper echelon of AQ enough credit. Of course Jihad Joe is a raving idiot who just wants to "martyr" himself so he can get his 72 virgins. On the other hand, I think that the leadership is smart enough to use strategy. Strategy dictates that you don't just go in guns a blazin'. Position your forces for maximum simultaneous distruction. Use force multipliers by having secondary terror attacks ready for use immediately after to initial strike to rachet up the terror. AQ knows they only have one shot to get the "big one" right, and I think they are carefully trying to get all of the pieces in place.