One thing that I often see when keeping an eye on social media during Jeopardy! time is people asking: “Why are players allowed to be grammatically incorrect when phrasing in the form of a question on Jeopardy!?” (An example would be saying “What is John F. Kennedy?” instead of “Who is John F. Kennedy?” when responding to “This man won the 1960 Presidential election.”)
There’s a pretty good reason for that: Time.
In the introduction to “The Jeopardy! Book”, Merv Griffin writes:
During its development phase, one aspect of Jeopardy! that appealed to the network was its humor, a fact that might surprise you since, even though Alex Trebek is a bright and witty man, Jeopardy! is not known as a hotbed of comedy. What happened in our early run-throughs was the answer-question reverse led to great fun. For example, if the answer was “Island that sold for twenty-four dollars,” the contestant often came up with “Where is Manhattan?”; we’d ask for a rephrasing and get “How is Manhattan?” No. “Who is Manhattan?” It became funny, in the small office where we did the run-throughs, listening to contestants arm-wrestle the language trying to phrase the response in the form of a question. Since the networks were queasy about the quiz scandals, the idea of a humourous question-answer show appealed to them.
As soon as we put Jeopardy! on its legs, however, I realized it was unfair and boring to badger the contestant about being grammatically correct for every question. We were getting only twenty answers into a game, because the contestants spent their entire time trying to phrase the question correctly. We weren’t ruling them wrong, we played with them until they got it right, but that idea went out the window. The show needed to be hard-edged and fast-paced if it was to endure, and it evolved in that direction.
In terms of why the show doesn’t outright declare it a wrong answer? The British version of Jeopardy! tried that for its Channel 4 and ITV runs. (There was a British version of Jeopardy!, you ask? That might explain how well that change went over.) Even the British found it silly, and by the time the show ended up on Sky 1, the “American” rule was in effect.
So, there you have it. That would be why as long as you phrase your response in the form of a question, it need not matter whether or not you use the proper question.