I am the guy who asks that question on every interview. You can hate on me now!
Let me clarify. I don't expect the candidate to get to the "a-ha" moment at all. I make my expectations very clear upfront so that the other side wouldn't panic. However, I expect to see how the candidate would approach the problem with the right attitude so I could get some insight of his/hers thinking patterns.
I personally wouldn’t mind if an interviewer asked me something in the lines of "how would you build a nuclear plant?", although I have no knowledge on the matter.