Mike - I have a bit of a problem with your use of the term "professional". It seems to me you are talking about performance rather than professionalism and I think we are looking at both performance storytellers who usually perform in the conventions of a structured setting and the non-performance storytellers who tell in more "low key" situations with "low intensity" in the telling.
It seems to me that at the end of your 5th paragraph you are not entirely correct when you suggest that these low key tellers are necessarily more casual in their choice of language, gesture, etc. I would suggest that the best of these teller use just as much artistry in telling the story and holding the audience as performance tellers in more formal situations. It is interesting to go back to Frankie's comments about how she learnt and applied her craft.