because a lot of people never knew (or could imagine) Stevie on the drums when they don't regularly see it (or nowadays, hear it).

as for the discussion above re: Prince.

he has two distinct voices: rhythm guitar (but as you said it, mostly in the late '70s/early '80s when he was playing the kind of music that needed it to survive), and the Linn drum machine. Immediately after hearing either, you know it's "Prince" (and the latter, is really what people try to imitate more than anything else when they want a "Prince" sound. It's one of the reasons I can sit through 10 minutes of Dam Funk noodling -- the "Princely" drums above all).

I'd also argue that while I couldn't really pick out Prince playing a keyboard solo as "Prince" as I could Herbie, Dukey, or Chick... except when it's that "Princey" stuff (see: "When Doves Cry"), the big "Prince" sound on keys is the voice programming.

to this day you have people (self included) trying to crack the code of those Oberheims to get the "horn" sound (I think it was programming + engineering on the recording side to get that out).