Also, Osama Bin Laden said that he did not command to throw the planes at the bridge instead of the towers (with would be dozens of times worse to the US, as it would cripple the local economy) because he wanted something that would be shocking, appear on the news and be remembered. And we all know how Al Qaeda is funded by the US for decades, so they might have told to Bin Laden to aim especifically at the towers because it would be more easilly marketeable as propaganda against the middle east, and would be less damaging then the bridge or the pentagon.