The absentia diagnosis is a bit like selling it to the masses. Normalising it, widening the bell curve of normal. eg if you cure Aspergers then you lessen the likelihood of producing hyperreal intellects like Edison, Einstein etc. It's spurious but it's not really aimed at the great thinkers of our generation.
I think it's also to do with our curiousity with the abnormal & different. Like our fascination with serial killers or depressive suicidal writers; they appeal to our sense of the fantastic, the unreal, the special or gifted eg Rainman.