I guess it depends on how you interpret the data. When I see a co morbidity in the range of 1% to 4% for a disease that has a background rate of 1% in the population my reaction is that Autism and ADHD have no link of any kind. The comorbidity can be explained away simply by looking at the background rate.
BTW I think you intended this as a reply to a post but instead made it a top level post.