May I please add one more consideration into this discussion. All references above have been to the type or class or aeroplane. I think that the need for a minimum ALSS gradient is driven more by the experience level of the pilots flying them. Typically, they are student pilots or GA private pilots with low overall experience and, probably, recency. If you put an experienced and current professional pilot (who routinely flies second order aircraft by hand) into this class of aeroplane then the same need for a minimum ALSS gradient may not exist. It would be interesting to relate stall and spin accidents in GA aircraft to the experience and recency of the captain as much as to the criteria being discussed here.