Geno had an interesting slant on this - he said a lot of the good young women coaches' first hire is a male assistant, they have a lot of success and the women move up, and the male assistants get hired either to replace them or to take over at some other mid major.
I do think men coaching women tend to hire female assistants at the college level and women do seem to like to add a male assistant - they are one step removed from in loco parentis with 18 year old college kids, so having that female/male combined authority may be more comforting to recruits - there are different issues that both boys and girls will be more comfortable dealing with either their father or mother about, and I think the same hold true in their transition to adulthood.
The issue is of course that the male sports are almost a closed shop, though a few enlighten coaches are finding that having a female assistant is a positive and brings something different to the table.