Dave Brennan's post gets pretty close to the truth, I think. (I may be prejudiced -- he's my husband!) But I think one problem that American audiences may have with unaccompanied singing is the intimacy of it. When there's a guitar or concertina, it's entertainment. When it's a singer by himself he is (a) taking a much bigger risk, and (b) asking the audience to connect with the subject matter of a song in a way that's much more emotional -- because unless he sings with intense conviction, the song will be deader than roadkill. That level of participation is asking a lot of an audience, and many Americans (I'm one, so I can speak) are uneasy with that much intense emotion.

There's a curious thing that happens with many songs in Irish, a habit that I think may have derived from the singer's need to distance himself from his material (like Joe Heaney in Dave's story above). Instead of using direct narrative to describe something that happened, in many performances the singer uses an indirect / subordinate clause -- so, for example, instead of saying "our boat was lost at sea" it would be something like "that our boat was lost at sea", as if it were part of a longer sentence that began "and the story goes..." I think it's a way the singers have found to remind themselves that what they're singing is a story. Some singers even go so far as to insert "he says" ad lib in their songs from time to time, for (I think) the same reason -- the singer wants to remind us (and himself) that he's just repeating what he's heard. It speaks volumes about the immediacy of this kind of singing that they need to do that.