Ok, lets look at this..
Does this rise (500%) include seizures, and the truly observable testable effects of autism or is this the 'spectrum' which can include so called higly functioning folks?
The definition of autism as defined on the autism website makes it clear that about 80 % of people with autism, as defined , have less than "normal" IQ, which is about 80. Thats not even 10 % of the population to work off of, starting off. These kids are barely teachable to begin with. Coupled with the seizures, and the rocking and othjer odd behavior,, autism itself is clearly a REAL, measurable, neurological disorder with hundreds of thousands of victims. (Does anybody say Down's Syndrome is a "fake" ?) And it is much, much more prevalent than 20 years ago.
As for the "spectrum", thats just designed to be scammed, especially for people looking for govt handouts like special schooling and so on. No denying that, but I would point out that Workplace disability is also a big government scam and in places like California there have been studies that as much as 40 % (!) of people on Disability are just plain faking it (ie walking with a fake limp, fake bad back, etc).... But I don't see Savage saying its 99.9 % fake (some of his listeners would scalp him if he tried to demagogue that handout)