This may be, in part, because girls and women with Asperger's Syndrome may be better at masking their social deficits than their male counterparts. Particularly, females with Asperger's Syndrome appear to be better at communication in general, may be more sensitive to the emotions of others, and are less likely to "act-out" in the traditional manner, thus making this population particularly difficult to diagnose.
Given the lower incidence of this diagnosis in females, there may be a fair number of girls and women who go through life feeling somewhat different and not knowing why. Even though these folks may be better at hiding their social deficits and may be able to appease any awkward situation by apologizing and shrinking away from the spotlight, these individuals nevertheless often feel different, confused and anxious in social situation. Specifically, females with Asperger's Syndrome may not have many (or any) friends, may feel that their interests are "weird", and/or "babyish", may appear to be more naive than their age group, may prefer to spend time alone, and may generally feel overwhelmed by even the relatively simple demands of daily life (particularly in social and performance situations).
Clearly, it would be tremendously beneficial for the clinical community to learn to recognize the characteristics of Asperger's Syndrome in girls and women in hopes of helping these individuals better navigate the often-confusing and at times, anxiety-provoking demands of the neurotypical world.
To learn more about Asperger's Syndrome in females please see Dr. Liane Holliday Willey's book (with a forward by Dr. Tony Attwood).