The concertina seems folkish because it's so rarely heard outside of street-corner Salvation Army bands. And even they are folkier than any concert performance.

The concertina's easy portability also suggests the sort of thing a carefree shepherd, gypsy, soldier, or sailor might carry with him, at least in a Victorian novel.

Steve, I call the Dubliners' arrangements "elaborate" only for want of a larger vocabulary. "Flashy" might work, but it sounds a bit dismissive. The quality of their playing really stood out in the '60s.