I could make up some mumbo-jumbo about case being a code smell and that it should actually be refactored to a method dispatch over polymorphic objects, but the truth is that I have no idea why I don't write case statements, I just don't.
Of course if I had to write that kind of construction often I'd probably learn the syntax of the case statement, but in the kind of work I do it hardly ever actually comes up.
You can't be a good programmer and forget the syntax of the language you are working in. If you need to look up something as fundamental as switch statement in the internet, it's like a writer looking up words in the dictionary before writing them down in his novel.
Actually pattern matching can also be described as something like a case-switch.
I do agree though that testing specific language skills is mostly pointless. The only time I've been given a programming test as part of an interview I was given a basic language spec that filled a couple pages then a book of problems to solve in the new language. Thats the way you should test programming skill in my opinion.
Give them a novel problem and have them solve it with a real computer and in tact syntax lookup. Then see what and how they did it and go over their reasoning. I'll hire the guy with the wisdom over the guy who can spit out syntax trivia flawlessly. Those are different skill-sets that do not predict each other.