I think the two of you are mostly in agreement. I believe mikecane is talking about someone that believes their mental model of users' needs, desires, and expectations is complete, and is using the question as a way to shut down a feature, with the implication being "if the reason someone might want X is not immediately obvious to me, it must not exist."
I don't think he was talking about someone that acknowledges that their understanding of users is incomplete and wants to learn more.
Yes. As an example, Jobs putting actual typefaces into the original Mac. Anyone used to the existing computing paradigm back then would have asked, "Why would a user want that?" Another infamous example is the marketeers at CompuServe thinking the CB Simulator was a bad idea -- and today we have something like it, called Twitter.
People like to chat with other people in real time. CompuServe's CB Simulator was a huge money draw for them (back then you paid per minute of connect-time).
I don't think he was talking about someone that acknowledges that their understanding of users is incomplete and wants to learn more.