I've been following the debate and its amazing how a term which almost everyone believes to know the meaning of can cause so much discussion. I agree with Graham that essentially it comes down to;
Form
Content
The content is, in theory, available to almost everyone in that most stories that one hears have been recorded and usually in a written form. For me what marks out the true storyteller therefore is the form, ie how they present the story. ( This is not to suggest that the content is not important ).
I'd like to expand but I'd better finish now and do some shopping etc (I'm at work ). I'll complete my train of though sometime tomorrow hopefully.