I saw a paper that was interesting, although the basis of participants was small, so it may not be completely true.
It said that they took around 20 people with HFA, and twenty with AS, with the same Full Scale IQ, and then looked at the areas they had problems in, their Perfomance IQ's, their Verbal IQ's etc.
They determined, that there was a difference, the HFA's did not have a significant difference between PIQ and VIQ. They also had different problems...
I'll see if I can pull it up. Although as I said, this is not a large study, and is probably not a global representation of how HFA and AS are Dx'ed. I have a feeling, if there IS a difference, AS and HFA'ers are missdiagnosed all the time!