As lots of other people have already said, the dividing line between AS, HFA and PDD-NOS is fuzzy. After all, each of these subtypes lie somewhere on the Spectrum. The autistic spectrum is like a colour spectrum, say, from black to white. Very severe LFA is dark black, while milder forms of autism are varying shades of grey. There comes a point where it is indistinguishable from normal variation (to extend the colour analogy, it's almost white but with a slight tinge of grey.)
Anyway, I don't think it makes sense to separate AS from HFA, but it does make sense to categorise autism in how severely it affects someone's day to day life. This seems obvious, but HFA is much more different from LFA than it is to AS, yet the current DSM implies the opposite. I'm all for a radical overhaul of the different groupings of autism, so long as people who are on the mild end of the spectrum aren't classified as NT.
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"Never try to teach a pig to sing. It wastes your time and annoys the pig."