Mmmm... I think it's more than that. It's been my experience that questioners don't always ask the right question. For example, consider the (not entirely) hypothetical "How do I implement drop-down menus?" What the person typically needs is some sort of navigable interface for a web site--but that's not what they ask for.
How is the root question uncovered? By asking questions. (Why do you need it? How far along is the project?)
The best solution answers both what they asked and what they should have asked.
The reason people do this (as you say) is that they sometimes have enough experience to suggest a different path altogether.