The DSM-IV puts it as:
Quote:
There may be failure to develop peer relationships appropriate to developmental level (Criterion A2) that may take different forms at different ages. Younger individuals may have little or no interest in establishing friendships. Older individuals may have an interest in friendship but lack of understanding the conventions of social interaction.
I guess they've been looking at all of the outcome studies where it shows most with an ASD are socially isolated, even as adults, and family members or roommates/carers are the only social relations the people have, and it's not appropriate and normal to just have these. Add in all of the other points, and you have the most typical/common representation of someone with an ASD.