I agree with all your points, but also think one must be circumspect when applying this sort of question. You're right, some people, when faced with a question

I agree with all your points, but also think one must be circumspect when applying this sort of question. You're right, some people, when faced with a question like this, will flounder. Maybe sixty percent of the population. The rest will all solve it in a similar sort of way. It's thus a bit of an "are you a complete idiot?" test, so by applying it you express an uncertainty over whether the person you're interviewing is a complete idiot. This is fine if you're interviewing fresh-faced undergraduates or something, not so good if you're interviewing someone with a long track record of success for a senior role. I don't interview people all that often, and the circumstances are such that by the time someone gets in front of me I can take it for granted that they're not a complete idiot. Thus, I feel no need to apply this kind of test.