While some psychologists like Isabelle Henault have written extensively about sex and Autism/Asperger's, it remains a neglected area of inquiry. While clinical observations will have to suffice, it is clear that we need more systematic study in this area.
My own observations are that sexual development is, well, quirky. People with Autism develop their sexual orientation, preferences, style independent of social or cultural influences and restraints. Growing up in social isolation, they don't come in to contact with typical influences, such as "what friends say" or what the current culture says about sex. But, this doesn't mean that sexual feelings (visceral responses, sensory experiences) are absent. As a result, people with Autism develop conditioned responses that may be quite unique or specific to their own experiences.
As clinicians, we can begin to dissect the history of development of a particular person to help them see how they have developed their unique sexual style, but we need to get to a point where, simply, we can talk (remembering comedienne Joan Rivers' line: "Can we talk?"). And this is tough for parents and people with Autism to broach (who wants to talk about their son's masturbatory materials?). But as we "put these issues on the table" we can better understand sexual development and, perhaps, be of some assistance in counseling them about sex.