Sometimes I wonder if some people (esp those who have never actually gone to Disney) are mixing it up with other theme parks - for example, we've also gone to Six Flags, which has a version of a
DAS, and for that you DO need a doctor's note. It's very strangely specific, though; the note can NOT actually say what the disability is, due to privacy laws, just that the person has a permanent disability that makes them unable to wait in lines (along with some other specific things I don't recall). But at WDW, we've never had nor needed any sort of documentation