Bin Laden makes no secret of his hatred for the United States, and openly admits anything he has done. He likes the credit, and so it would stand to reason that he would admit to something like this. It's just like a well-done paper that was passed in, but nobody has claimed. Some people would have no qualms about saying that it was their work.
And Americans stand to make a lot of money with all of that oil in Iraq, which is why, in my opinion, Bush attacked in the first place. The world was opposed to his invading even with the terrorist attacks. Imagine how opposed they'd be if it wasn't for the WTC attacks? I must say, I don't believe the planes brought the towers down. Was it Bush? I don't know, but, and sorry for the bluntness, it was mighty convenient for him, either way.