Cropdusters, cropdusters, cropdusters.
You misunderstand. The terrorists' interest in cropdusting had nothing to do with broadcasting anthrax spores. Nothing whatsoever...
The cropduster angle was only a back-up plan. Had Atta and the boys been unable to hijack commercial airliners and fly them into the WTC and the Pentagon, they would've heisted a couple of Agcats and crashed them into a Dairy Queen and a revival tent.
Don't over-analyze...