Go back and watch the video's of Osama and his buddies watching events unfold during that day. The translations of those video's showed that not only did they believe their attack was wildly successful, they never imagined either tower collapsing.
Pure propoganda. They would have been pleased with anything. Did the videos show their disappointment at not having flight 93 succeed? They needed to put out a message about how great they did - no matter what.
I always believed that those camel f-ers thought that flying the planes into the towers would knock them over killing more people on the ground. They might have figured out how to fly a plane without taking off or landing, but have no clue about physics and mass.