Author is laughably clueless about history. Crossbows date back to the 5th century BC (in both China and ancient Greece), long before the invention of plate armor. Also, mounted knights in armor collecting taxes? Sure, just like the IRS sends tanks instead of demand letters...not. Historically medieval armies included heavy cavalry like knights and crossbow and longbow archers.

http://en.wikipedia.org/wiki/Crossbow#History is not exhaustic but reasonably well referenced.