I think this is really what it is. There's this trend in the valley of everyone thinking they need ninja zombie pirate rockstar gurus who can solve P=NP and interviewing accordingly, when they're really writing simple CRUD apps and just need someone that knows how to do solid architecture and design.
Asking stupid questions like golfballs on a bus sends a signal of "we need geniuses for some reason" and is intended to make the candidate think "wow, the interview questions were so hard, everyone that works here must be really smart!"
It also means that the person asking the interview may not be the technical hiring manager. I expect such questions from someone in HR, but not from a technical hiring manager.
Someone in HR most like can't judge the answer to the question "How would you scale X, given Y and Z", nor could they come up with such a question that is appropriate for the position in question.
Such questions do more to isolate the variables, (1) the job to be performed, and (2) the interviewer's ability to judge the answer to a question relevant to the job. I can really only see such a question being asks by somebody that doesn't know why they are doing the hiring in the first place.
Judging by the responses in this thread, such a question is controversial, especially among the type of people that make up the HN community. That alone should be indicative that such a question may result in a high rate of false negatives. You probably lose more good candidates than gain.
Perhaps, you think that a direct question about realtime monitoring systems isn't tricky enough?