Can only relly comment on HFA and Aspies but...
I also was very "odd" at school - same as dd (who is being assessed for ASD) but it didn't matter so much as I was at an all girls grammar so far less of the socialising, no boys to deal with, several other "wierd kids", and we all sat and listened in lessons and then did questions etc. Also being "odd" was accepted. Now all kids go to comprhensives, in mixed classes, and the social aspect is far more important. My daughter is expected to do "group work" in school, I never had to so the fact that I couldn't didn't matter. Also I look at the stuff dd brings home - it is all dressed up to make it "interesting" to the NT kids but all the pictures, silly titles etc actually distract dd who can't do the maths questions on tables because she can't work out how the elephant fits in - well neither can I but I didn't have an elephant with a sum on its head when I went to school, just a list of nice clear questions.
So in all I think that there is far more emphasis placed on "group work" and "fitting in" in school and that an old fashioned cirriculum and lesson style suited Aspies and HFA but the modern "fluffy dressed up questions" and "group work situations" really does not work for many on the ASD.
Finally I think that society is now far less tolerent of difference and far more into everyone being social. In the old days people could try to fit in when they choose to socialise and then have "time off" at home. Now with moibiles, facebook etc there is constant pressure to socialise all the time so life is far harder as even people with ASD still want some friends but now keeping them seems to require an ability to constantly reply to texts, send them etc which it didn't before.
So I think that actually being on the AS, certainly at the HF end, really means that there is a mis match between how you are and how society expects you to be and "how society expects you to be" has contracted hugely so lots of peopel (and children) who would have been called "odd" are now not accepted for what they are but labeled as autistic.
I'm not saying that these children do not need help - far from it - most people want friends but the problem now is that people, other children, society, will not accpet difference so all the associated problems with ASD - like depression, inability to hold down a job etc are gettign worse - not because autism is, but because society is.
Catkinq