Metal and whiskey
It occurs to me that, from a point of view, Metallica in the pre-Black Album era was basically a folk band; they produced straightforward recordings of easily transcribable songs, and owed much of their popularity to fans who liked to play those songs. It also occurs to me that by the same standard, Iron and Wine is not a folk band, but a pop band working in a folk style; "Radio War", to pick an example, is a beautiful recording, but I have trouble imagining my parents sitting down in the living room and harmonizing on it.
On the other hand, my parents aren't big indie-rock listeners anyway, so that might not prove anything.