Generally speaking, unattractive people often compensate by being competent (or, to put it another way, attractive people often feel that their attractiveness entitles them to forgo competence). That isn't to say that some people aren't both attractive and professionally successful, or that it isn't true that many people are neither, but there is a phenomenon where many attractive people are less motivated to make something of themselves because society tells them that they've already got it.
Because of this, in any competitive and accomplished field of people, you'll generally find more unattractive types than in the general population.
Now, as for the gender thing, there are two major things that I can think of feeding into that. First, how accepted a woman is by society relies more heavily on her physical appearance than it does for a man; in contrast, how accepted a man is by society relies more heavily on his career and income than it does for a woman. Because of this, a physically attractive man is less likely to feel automatically accomplished by being physically attractive than a woman, and is more likely to pursue a competitive career despite this. By contrast, an unattractive woman is in more of a pickle when it comes to social acceptance than an unattractive man, and she may be more motivated to compensate as a result.
But, regardless of factors that might cause a gender discrepancy, I think this phenomenon impacts both men and women, even if it doesn't do so equally (it would be silly to pretend not to notice how geekish guys tend to concentrate in highly qualified careers, and it would require a rather small mass of social experience to have somehow managed to avoid meeting any attractive, accomplished woman in one's life).