I think the most unique notion (which has already been suggested) is that dwarf women DO grow beards, but keep them shaved for various cultural reasons, i.e.:
-In imitation of humans or other humanoid species. If interaction between humans, elves, goblins, etc. is advanced enough that they are actively trading and occasionally traveling together, its very believable that cultural bleeding would occur.
-In a related sense, as a specific caste; a way of distinguishing sex, heritage, employment, or social rank. This is a more adaptable system, and could lead to some interesting conflict within dwarfish society. Humans have fought wars over lesser things.
-As an analogue to humans' sexual dimorphism. Again, like someone else pointed out, beards may be a symbol of male sexual status. A lack of beard, however, may be the more distinguishing and provocative feature. Another thing to consider is how human women have, over time, become more childlike in their features as adults (consider how the domestication of wolves has lead to dogs with more puppylike features). I'm not sure if Toady has children growing beards or not, but it is something to consider.