Jack Campin had it (several posts ago). I'm sure it's a temperamant thing (that's the temperament of the piano, not of the people hearing the songs!) - just gives the typical trad tune a completely different feel - compounded by all the overtones and upper harmonics from the multiplicity of strings on the piano. John-in-Kansas had some very erudite stuff on temperament in this forum some years ago which I'd like to read again if only I knew how to find it. I think it's the basis of many interesting things - eg why an "a capella" folk trio such as Coope Boyes and Simpson sound like more resources than the Huddersfield Choral Society, and exactly why tunes of a certain character - especially a modal character sound so different on the piano. I'd challenge anyone to accompany "Gathering rushes in the month of May" on the piano without totally changing the feel of it. Also explains why so many sub-classifications of "folk" sound absolutely ok on the piano - they are harmonically based, so are comfortable in equal temperament.

Just guessing really.

SJ