If the plot is a machine that allows you to get from set piece to set piece, and the set pieces are things without which the reader or the viewer would feel cheated, then, whatever it is, it’s genre. If the plot exists to get you from the lone cowboy riding into town to the first gunfight to the cattle rustling to the showdown, then it’s a Western. If those are simply things that happen on the way, and the plot encompasses them, can do without them, doesn’t actually care if they are in there or not, then it’s a novel set in the old West.
