I don't see it as superstitious.
a) If they attack again this year, it wouldn't be the first time that terrorists struck on an anniversary (OK city, one i can think of). So, I do think it's rational to be more worried that day, just like we were more alert on July 4th. There seems to be a lot of symbolism involved with terrorism. How great would they think it was if they pulled off another 9/11 in spite of possibly heightened security?
b) I wouldn't want a birthday on 9/11. Who wants to celebrate on that day? And I've had 9/11 comments made about my birthday, and it's a week later! I'm sure the 9/11 date shock will fade, but for now it doesn't seem to be a good day to plan a birthday or anniversary.
c) this has to do with (b) - I wasn't around during Pearl Harbor, obviously. But was the actual date so widely-discussed then? We now call it "Pearl Harbor," not "December 7th." Unless we come up with another name for 9-11, it will be "September 11th." No one will ever forget that date. We all still remember "Columbine," but do we remember what date it was?
d) elective surgeries - I would rather see all the memorial events that will be occuring and have the surgery another day. They also might be worried about more attacks occuring [see (a)], which I consider logical rather than superstitious.