I wasn't aware until fairly recently that some melodeons were tuned to Bmaj instead of Bmin. I borrowed someone's Hohner and was several bars into Billericay Dickie when it all started to sound a bit strange!

Given that we're talking about a D/G melodeon, and that the relative minors of G and D are Em and Bm, does it not make more sense to have both of those minors? I think I might have difficulty playing a melodeon tuned to Bmaj rather than Bm.