It's fun because the myth collection was almost a side effect of the linguistics work: it shouldn't be a surprise that when the Brothers Grimm walked into a small village and asked for the oldest documents the village could find they got a lot of interesting myths and fairy tales in return. There's a bit of dramatic irony that Grimm's Fairy Tales has had such a homogenizing force on the myths since its publication when a lot of the reason for collecting them in the first place for the Grimms was seeking all the little nuances and differences and distinctions between them (including and especially linguistically).