I think bin Laden believes what he says. He hasn't spent much time in the west, or out of his cultural sphere. He's just crazy, and needs to be put down. He's very serious about this jihad thing. Just as Hitler was about his beliefs.
He gained his influence due to his money. Money always helps.
I thought he went to Oxford. Am I remembering wrong?
Also, I am pretty sure that a plane will not instantaneously depressurize if hit with a stray bullet, especially if the ammo was frangible. I saw someone post a very good explanation of why this is on a thread but haven't been able to find it this evening. In a nutshell, he explained that planes already have open pressure valves in them constantly controlling the release of air, so if more were to start leaving, those valves would close to make up the difference.
Sorry I can't find you a link at the moment; I'll post it if I do.