"somme versions include cliches such as the milk white horse/steed. "

Should the familiar phrases in ballads be considered cliches, or are they an essential part of the ballad structure? From a singer's point of view, they make it easier to remember the song, and help to carry the story forward for a line or two without too much effort, allowing you to focus on the material element of the story which comes next. This probably helps the audience too, knowing they are on familiar ground and can relax for a moment.