"It just happens that certain keys have common characteristics both on woodwinds and strings. Playing in A, you will use three of the four strings on a violin open, so that'll give you a brighter effect."
quote jack campin.
if you are going to use open strings on the fiddle, and playing in A as an example of a brighter effect , You could then use the same argument for the key of G on a 5 string banjo[tuning Gdgbd], in which you use five strings open or for a guitar tuned in dgdgbd