Servos - Coreless or Digital?
The PCM signal has more encoded "bits" of information, which, once all the computer-geek rhetoric is finished, translates into more servo resolution.
The way it was explained to me, running digitals on PPM would be a waste, since you truly could not tell the difference between digitals or analog. That may be where the "conventional wisdom" comes from.
I dunno; I haven't tried digitals on PPM.
Steve