Put this down under the heading of 'he's not a doctor, and he shouldn't even be playing one on the web'... But having said that, the following is meant in all seriousness.
Consider the list of people who've come down with inhalation anthrax. Do you notice a pattern? They're all on the old side. This page in the Washington Post identifies ten cases of inhalation anthrax, and gives ages for eight of them.
The ages are 61, 63, 55, 47, 73, 59, 57, 56. (The first four have died; the second have either recovered or are still sick) Granted, 47 is hardly old. But when you consider that these were mainly in workplaces where you're not going to have a lot of people in their 60s, 70s and 80s, it's a pretty striking pattern.
Compare to the ages of those who've gotten skin anthrax: 51, 38, 1, 27, 30, 35.
Doesn't it sort of sound like maybe there are a number of other people who've also breathed in a bunch of spores but had younger and better immune systems and were able to fight it off?