I have little doubt that he would spray the entire USA today if he could.
The only reservation I have is that he might be holding back on another big attack for the first bomb to fall. That would have some strategic terror value in (his mind) making us reconsider the wisdom of fighting him.
Not warning shots, per se, but bin Laden employs a low tech, high-failure rate approach, rather like the new NASA strategy for planetary missions. Remember that the first attempt to take down the WTC towers, back in 1993, was a flop: the terrorists hope to topple both towers and spray cyanide gas all over lower Manhattan, killing 200,000 people, but instead both towers remained standing, the cyanide simply dispersed harmlessly, due to the explosion, and only six perished. Anthrax is a frightening weapon, but a hard one to deliver effectively. The crop dusters that Atta & crew were inquiring after would be a relatively poor delivery system, but probably something that bin Laden would be happy to work with in the interim. Of course, the fact that there has so far been only one case does not preclude other fatalities, but the lack of a rash of cases implies either that this was a test shot or accidental spillage, or that they didn't use a very effective delivery system.
It would be easy to give it to one person. It would/will be very difficult to give it to more than ten or so at a time. One thing I thought of - you hand someone a bouquet of flowers and have sprayed the top with spores. Most of us stick our nose into flowers and take a deep breath. That's a very effective way to get a lot of spores into someone's respiratory system.
And that is what you would need. A lot delivered at once, for someone to get sick. If we're walking along a street and someone sprays it from a rooftop, we're not going to get sick. They tried this in Japan and it didn't work. We have these nose hairs which are going to catch a lot of the spores and keep them from being inhaled. A few inhaled is not going to be enough.
Anyway I think this man did get anthrax from a terrorist source. I don't believe they have the ability to engineer the bug to make it penicillin resistant and I don't think they would try - inhalation anthrax is typically deadly no matter what antibiotic is effective, so why bother to make it resistant?
I also think they just gave it to one person, because that is about all they can manage, and because it was one heck of an effective scare for us. Scaring us is what they are about.