MTed: that is not a simple answer, it is merely further complicatimg the issue by offering yet a new meaning for modal. And a completely incomprehensible one at that. What do you mean exactlY?
   Most people would say, for example, the Old Joe Clark is a modal tune. You appear to be saying that it is a modal tune if someone plays it with a drone accompaniment, but it is not a modal tune if they accompany it with guitar chords. I'm sure everybody else in the world but you(MTed) defines whether a tune is modal or not according to the scale it is in, not according to how you choose to accompany it.