My final theory is that anything that sacrifices real shootability for conealment is a "snub". A 2" and below gives up velocity and sight radius, as well as positive extraction in exchange for being more "packable". In general people don't buy 2" and below revolvers as a first choice for a "range gun". They were made to be carried.
The 3" is a short barreled revolver, IMO, and was an attempt to make a service revolver that could be carried more easily by plainclothes LEO's and govt. agents, and became very popular with civilians. I don't have a 3" S&W but do have a 3" Ruger GP100, and it is not a snub to me. It's a medium frame .357 with a short barrel.