Fats have an amazing ability to be willfully ignorant and gloss over facts in their never-ending quest to justify their gluttony; see for instance their recent declarations that "calories are a myth," etc.  Therefore I can see them just as blithely claiming that PWS doesn't mean they're retarded and ignore that actual PDWers will in fact eat themselves to death, as you said, which is what non-PWS fats are doing anyway.