His point was hardly that we should design interfaces for computer illiterates, but that a person who has never used a computer may provide valuable information

His point was hardly that we should design interfaces for computer illiterates, but that a person who has never used a computer may provide valuable information on how humans try to approach new interfaces in general. This information can help us put emphasis on the right things: Instead of a bunch of buttons, concise text that leads the user. I imagine something like "Your first time using Internet Explorer? Click -here- to get more information." would have helped him greatly. (not in this particular situation, but if he were at home with his newly bought computer and properly invested in his pursuit of email, then yes.)