I'll bet every one of us went to school with at least one, and probably several, kids who were considered odd. We all could see they were socially inept at some level or another. They were often bullied and called nerds or dweebs or geeks or losers or goodness knows what else. Some of the more severe cases were classified as "retarded" or whatever was the PC label of our generation, and placed in special classes. Very few, if any, of those people were diagnosed as having autism spectrum illnesses. Now society understands more about this kind of disorder and many people with autism spectrum disorders get appropriate treatment, and hopefully less social abuse.
I have taught or tutored several boys in the past couple of years with Asperger Syndrome. They are all functional human beings and will be able to get jobs and raise families, although it will probably be harder for them than most. People like this have always been out there, they just weren't diagnosed.
It's easy for me to see that the diagnosis rate has increased hugely, especially of the less severely affected people. Does that explain the entire increase?
And how many kids did you know at school who were drooling, rocking back and forth, unable to speak, climbing the walls, hitting and spitting. Were they all really misdiagnosed (the answer is a simple NO, because the rates of MR and other 'misdiagnoses' have stayed more or less the same over the decade, ie have not fallen). Were all those kids in special schools? (again records show that wasn't the case).
What you describe is Asperger's or a very mild end of the spectrum. Those previously missed cases could account for the some of the increase, but in no way explain all of it. Quality studies are clear on that, ie taking into account milder and moderate/severe forms.
Bottom line is that you in no way could EVER miss a moderately affected child (let alone a severe one), for the simple reason that such a child could never go through educational system unaided. And better diagnosis of mild cases simply does not account for the increase. Go figure.