Believe me I have no doubt that the scenario you described would be devastating. I was just pointing out how in-effective a man with a big 'ol bag of anthrax really was. Delivery is the sticker here. The scenario you expained is one for worry, but it would be a massive effort by operatives in various cities to pull it off. It's just that so much has been made of how little bio/chem agent it takes to kill millions, and while that is true if everyone lined up for an injection, in a real-world scenario, it would take a herculean effort like the one you described to be an effective attack.
I don't think it would take a herculean effort to kill thousands and utterly destroy our economy. Ten Islamikazis in ten cities could do it. They each begin their day dropping 100(invisibly) leaky anthrax laden envelopes in mailboxes, and sending a few FedEx and UPS boxes.
Then they move to the subways, and toss glass jars of spores on a couple of the main lines, the subway trains' rushing through pulling a vacuum ensure dispersal to dozens of platforms and up onto the streets. Plus, its a perfect environment for spores to survive.
Finally, they go for their main targets, sports arenas and major office buildings where they break into fan rooms and break anthrax jars against the air intakes.
If they accomplish half of this, our economy will be totally wrecked.
That is just ten jihadis with 20 one kilo glass jars each, taken from just one hidden cache prepositioned by Iraqi agents (who never know what is in the heavy boxes).