Interesting question. One possibility is a heuristic to determine whether the user is looking for a broad overview or trying to solve a specific problem. For example, "2d arrays in Objective C" should bring up a doc page or a tutorial page that provides an overview of the concept; but "How to initialize a 2D array in Objective C" could provide an SO page where someone has asked exactly that. In general, the narrower the query, the more likely it should be that a forum or other UGC site will provide a better answer than an overview page, because someone else has likely run into the problem before.
There are some of us who don't use 'how', 'why', 'where', 'when' as a carry over from the older days when such terms used to just be ignored. So your example would be searched as "initialize 2d array objective-c".