the entire building would have been destroyed. They essentially crash-landed next to it. Dive-bombing would aim for the center of the ring, filling it with burning fuel.
In general, people here ascribe a lot of decision-making capabilities to al Quaeda. I think bin Laden is doing the best he can. He is a fearsome opponent, but his ruthlessness lever is all the way up. He can hurt us badly, but he has no reserve, no capability to escalate at will. Of course he will try to do something even more spectacular next, but I just don't se him timing an action. It's too dangerous, especially now that US is so alert.