Poppycock. Another case of IAD controllers being completely out of touch with reality. I can prove geometrically that an aircraft did not "reverse course on the runway" by exiting on a high-speed. The AIM is not regulatory anyway, so it's not like they can violate you by using this paragraph. Unless you purposefully disregard an instructon from them NOT to use the reverse, they can cry to you about it but the argument has no teeth.
link to a discussion about this issue (note: conclusion is that unless SPECIFICALLY prohibited, via published or verbal instructions, it's not an unauthorized maneuver)
http://www.propilot.com/doc/bbs/msgs/9929.html
sorry to obsess so much, but IAD pisses me off.