The FBI is avoiding the whole issue by using the word "terrorist" very specifically to mean a person who is part of an organized group that has planned a particular attack. In many cases,what we are seeing now are isolated Muslims who have perhaps been encouraged by their local imam's hate-filled ravings and by the hate-filled ravings in their own "holy book," but they are not part of a larger group. Hence the FBI can avoid using the word "terrorist."
The fact that AQ has repeatedly called on Muslims all over the world to start staging individual attacks is not relevant from the point of view of the FBI, of course. They're just lone wolves, disturbed individuals, etc. But believe me, if this had been a lone wolf attacker of any other kind, the FBI and the press would have been all over it. The Columbine killers were analyzed up one side and down the other, with their video games, internet contacts and other influences endlessly discussed (even though one of them, the dominant one, was obviously seriously mentally ill and his family had been seeking treatment for him prior to the attacks).
This Bosnian may have been crazy - but it was his ideology that led him to express it by blowing away 5 random Americans doing evil things like buying Valentine's Day cards (Muslims hate Valentine's Day, for some reason, and many of their nuttier mullahs have launched campaigns against it in their countries).
Another Freeper called it "Sudden Jihad Syndrome".