It's an age-old debate, with much disagreement over the differences and the question of whether or not there's any difference at all, or are AS and HFA the same thing (with the word 'spectrum' accounting for said differences and variations). The main difference in the diagnostic criteria is that for HFA you have to have at least one thing from the language section in the DSM. (That section isn't in the AS DSM.) But I've seen studies that basically said almost all people on the spectrum, even aspies, fulfill the language criteria. In that case everyone should be dx'd with HFA and AS wouldn't exist... The DSM is due for an overhaul soon and I'm guessing the criteria will change and hopefully it'll be more accurate/true-to-life this next time around, possibly addressing other traits that aren't currently in the criteria.