Another thing I think people need to remember.... While there have been many other events that some may rank higher than 9/11, this is one of the first times such an event was captured from so many angles. Not only did mayhem take place, but Americans watched it unfold live, and in good quality too. If a bomb goes off in a train station, odds are the only footage you will see is from a security camera, and then news report footage of the aftermath. I think that's the key, seeing the destruction after the fact. Watching the events of 9/11 unfold before our very eyes, the uncertainty of whether or not you were safe, and fearing how many more may be killed in the coming hours, leaves a much stronger memory in someone's mind. Lets just say the towers were around in the 50's and the same event took place, I don't think it would have impacted Americans the way it did ten years ago. Knowing a serious event happened, and watching a serious event happen will greatly affect how people will remember the day.