The Americans celebrating bin Laden's death confounded me in many ways, but one of them was that level-headed Americans had come to the conclusion that bin Laden and al-Qaeda were no longer a really, really serious threat to them personally. Despite what mentalfloss says, the U.S. mission to destroy al-Qaeda has been largely successful (and that was the main mission, or at least the important mission/Bush had this grander idea of spreading democracy and fighting tyranny no matter what form it came in). Al-Qeada can't seem to launch major terrorist attacks on the U.S. itself anymore. Sure, there are followers and sympathizers who make bombs, hide them in their clothes, and can't make them explode when they are supposed to. But they're just people who have never been trained by Qaeda. They just do it on their own.
As 9/11 became more and more of a memory, most Americans did mature somewhat about terrorism and being threatened by it. That's one reason I'm puzzled by the celebrations of bin Laden's death. It couldn't have solely been a sign of relief because Americans weren't as threatened by al-Qaeda as much as they used to be.