ShockWave
A thought. Attempts at providing the sort of spiral stability effects of which you speak by natural aerodynamic means (ie the shape of the aeroplane) while not impossible would very likely compromise other very much more important things like cruise efficiency and low speed high lift capability. If I were part of a FBW design team I would be pressing for the (highly desirable) characteristics that you speak of to be provided artificially by the system. Do you think this is what is in fact going on and the manual is merely describing these abilities that the FBW system provides by using stability terminology?