Sorry, I should have elaborated on this, because I certainly haven't forgotten about Bob Stevens.
My point was that this report suggests a difference in the long-term effects of the different batches of anthrax: the NJ anthrax caused long-term effects (fatigue, memory loss, etc.) that were apparently not caused by the FL anthrax. Stevens' death doesn't bear on this issue: since he didn't survive his initial bout, we have no idea what long-term effects he would or wouldn't have suffered had he survived.
The big dividing line among the people who developed symptoms of infection is a simple one. All the deaths occurred with people over 50.
This group of people has substantial ethnic diversity. It could be that some populations have a degree of inherited immunity.