[kevhito]

I apologize. I didn't mean to suggest we should design for a "typical human" (even if such a thing existed or could be well defined), and I agree that we should design for a range of user abilities. I was trying (poorly) to discuss their definition "disabled", which seems unhelpful as it seems to be synonymous with "human".

[adisinom]

The definition suggests we should focus on the context that disables people -- the mismatch between abilities and affordances, because as you point out, disability being part of humanity isn't a useful result.

For example, until the mid 20th century, deaf people in Martha's Vineyard might have been atypical (0.7% of population) but because islanders used MVSL, deaf islanders were not disabled. Later conditions changed, sign fell out of use, and deafness became a communication barrier.

Sure, if more people were deaf, Martha's Vineyard would still use sign. But deafness itself is not a sufficient condition to be disabled... rather the direct cause is society.