NASA icing video says "avoid use of the autopilot in known icing conditions". But the Q400 manual only says this in the event of "severe icing".
Seeing as use of the autopilot masks ice-induced changes in aircraft behaviour, how are the pilots meant to be able to gauge the transition from moderate icing to severe icing? I would guess NASA recommended hand-flying in all icing conditions precisely because the transition from moderate to severe could be difficult to perceive, especially in a high workload phase of flight.
Guessing wildly here, but it looks to me as though a dispute between FAA, NASA, manufacturers and airlines about which icing policy is best may have been resolved, as so often before, by a large pile of corpses.