Well, besides the fact that he was the President, it was probably more the idea that a reasonably young man with a lot of promise(and an exceptional amount of that hard to define stuff called "Charisma") was who was gunned down.
(that's my take anyway...I mean look at all the press that Heath Ledger's death has received recently for some reason, and I can only surmise that it was basically for the same reason...his relative youth)
