To help guys shopping for their spouse/girlfriend? A lot of men have not based their whole life on knowing that the D is the biggest.
FWIW, D is NOT the biggest. DD/E, EE/F... even GG... aren't the biggest. Theoretically, there's no "upper limit," but when you're talking about retail stores like Vicky's, I can tell you that while they do carry DD/E, the selection is very sparse.