I like how they asked a map-reduce question. If your previous experiences didn't involve working over massive datasets with distributed computing, you wouldn't have a clue. But if you did your search about your prospective position, you could find and study for the potential interview topics.

They are effectively selecting candidates who have spot-on experience for the position in hand or are willing to put the time to study for it. Is it too much to ask? Probably not for what you would be getting in the next couple of years if you were to keep it up.