Yes, the diagnosis of autism is on the rise. However, as the federal Centers for Disease Control and Prevention puts it: "It is unclear how much of this increase is due to changes in how we identify and classify ASDs in people, and how much is due to a true increase in prevalence."
The candidates talked about autism in the context of Gov. Palin's child. The prevalence of autism isn't a campaign issue — they both agreed it was on the rise. The only parrying here was that Obama said an across-the-board federal spending freeze would prevent researchers from spending more money to understand autism. Of course that assumes that the National Institutes of Health would not be allowed to reallocate any of its funds — not necessarily so.
NOTE: Governor Palin's youngest child has Down Syndrome. In tonight's debate, the topic of autism came up in the context of discussing children with special needs.