Not necessarily. These guys are smart and cunning, and they may well be waiting for a special moment or for us to perform a certain action before they play their ace. I can think of many huge sports, entertainment and especially political events that would fit their grisly bill. They will only get one shot at "the big one" so if they have it, they will want to get maximum effect. Yes I am wearing my tinfoil now 24x7.
I think they took their best shot at us on 9/11. They had to know that security would be tighter than tight after that.