every song does have an instrumental version, yes, but in this case, these instumentals were demos that were recorded by the band, presumably before Morrissey worked out the vocal portion of the song. i think there is an appeal to hear them because they represent a very early stage in the creative process. it's kind of like getting your hands on a pencil sketch of Picasso's Guernica, drawn in his sketchbook before he started working on the final painting. (although i'd much rather have the latter! :)