One person makes the claim over at his response to the Quora question Do people with Asperger's have above-average IQs simply because the ones with below-average IQs simply get diagnosed with autism instead?.
No.
Intelligence testing as most neurologically typical people understand it, is heavily biased toward individuals with expressive and receptive language ability which is often impaired in persons with autism to a greater degree than in persons with Asperger's.
As an example: imagine an intelligence test that was written in English being administered to a person who grew up speaking French. That person might be quite bright but would likely score very low. There have been numerous documented studies of the effect of language bias in intelligence testing that makes the idea of standardized intelligence testing a questionable endeavor.
From personal experience, my own son has rather severe language impairments and, if tested with a written or verbal test, would almost certainly have an MR diagnosis in addition to his autism. However, when tested with strictly non-language based testing methods, has proven himself to be quite bright (in the empirical sense, that is. Watching him spend 30 seconds on a strange computer before finding his favorite YouTube videos shows that he knows quite well what he's doing).
Is he right when he says that "Intelligence testing as most neurologically typical people understand it, is heavily biased toward individuals with expressive and receptive language ability which is often impaired in persons with autism to a greater degree than in persons with Asperger's."?
And could IQ tests be biased against Aspies in other ways? Could they also be biased in favor of Aspies in certain ways as well?