r[revision number] just sounds silly.
The Shadows and Shaders Update is the official name, but isn't worth typing for some people.
S&S sounds silly as well.
v21 rolls off the tongue and people prefer to call it that since it's a large update. At least people know what we are referring to, even though it isn't official. No need to get riled up because people aren't calling it what you want to.
