I'm part of a German forum and going with the stereotypical German attitude, many answers to those duplicate posts are very direct. A "how did you adjust to life in the US?" or "what vacuum cleaner is the best?" is often answered with "why don't you use the search function - we've already answered that a gazillion times!"
Makes sense to me too, but then I talked with a newbie in person who reminded me that not everyone is computer-literate, not everyone understands the "common sense" rules of a forum, and sometimes phrasing those seemingly easy questions is a way to enter a forum group without committing too much.
Answering in a direct way can be very affrontive and push the poster away and make them shy away from posting again. Not answering is kind of rude too as the poster obviously wants the question answered. One option is to link another thread or to simply answer and see if the topic takes off.