MtheGm,
i must look that thread up.
I think the point more precisely is that the guitar and more importantly its precusors have a much longer history than the concertina,which is essentially a modern invention.
"Scottish traditional music has been played on the guitar for well over two hundred years, at least that is, since the publication in Edinburgh of Robert Bremner's Instructions for the Guitar of 1758."
The interesting issue is that among the non folkie public the concertina seems to be perceived as the most traditional of instrument. the reason for this remains unclear to me.
john