I agree, they should have the entire rulebook posted on nfl.com in pdf form, I agree since the rules change so much they should give the fans access the complete rule book.
Note that last sentence: The contact by the defense player must be the cause of the runner going down. Hasslebeck was already going down before the incidental contact and was no longer in contact with the defnder when he hit the ground. Unless this is an outdated version of the rule, he was not down by contact when he hit the ground and subsequently fumbled. The original call of a fumble recovered by Pittsburgh should have stood.