Thanks for all the interesting replies.

No one has yet contributed a reason why the 'folk hold' might be an advantage over the 'classical hold' (with a modern instrument). I guess it's probably just tradition, then, that causes so many folk fiddlers to play that way.

I agree, there are many fine folk fiddle players that do use the 'folk hold'. So it seems that, while the 'classical hold' does have a number of advantages, the 'folk hold' is no bar to becoming an expert fiddler!