Hmmm.... I guess I don't see terrorism as a crime, exactly, but as an act of war. Different rules.
Well I agree that as a concept that foreign terrorism is an act of war.. But what of domestic terrorism? What of OKC or the Unabomber? Also, it _is_ a crime under federal law.
Whether we treat an act of terrorism as a crime or an act of war is the same as asking whether we put the perp on trial or shoot him in the head (or ship him off to gitmo). That there is a federal law against terrorism, though, shows that the government is (in some cases) prepared to treat terrorism as a crime and not an act of war. Or at least, a crime first, and an act of war second.