Thanks Howard and Jack. Howard I never thought of that! Look for the simplest solution I suppose. It makes sense that one singer might use that technique to close his tune, and others copy him or her.
Do you have any evidence that this may be an Irish musical characteristic? My reason for asking is that most of the Southern Country singers tended to have Irish songs in their repertoires. That said there is a strong Scots connection to Dorset song as well. (See my article in Living Tradition)