There's a parallel talk into it chapter about gender gap. This gap is part of a larger gap involving software development in general; there are few programmer women. I presume, that this highlights a similarity between wiki and a software development environment; and really many from most enthusiast, and productive contributors are too programmers.
But... as you know, the profile of a programmer is far from the profile of a woman; consider the famous statement "The three chief virtues of a programmer are: Laziness, Impatience and Hubris.". Then consider the pedia statement "Be bold!", that is a gentler way to name "hubris". :-)
Is gender gap so mysterious?
Alex