I don't think that's fair. You don't know how useful a feature will be until its implemented and in users' hands. You will have a guess, of course, which is why you implemented it in the first place. But you don't know. And surely, a certain percentage of the time, your guess will be wrong.
Unless you ask.
Again, I think you're being unfair. What people say and what people do are not always the same. People may say "Yes, that's a great feature!" and then not actually use it when it exists.