Good points in previous answers, which I mostly agree with, but I will add my two sour cents.
The answers as it was mention, are pretty flexible in their content, but so are the Questions.
Which questions are fit for WB is not determined by some strict borders(like facts or attributes, field of knowledge), field of Questions have soft not defined borders.
As result Q are closed and put on hold based on -- do WB users like question or don't. If we like a question, it stays and get answers because it is likable, it we do not like the question it is closed.
So to check the real situation and stats probably closed as broad should be included(a bit hard as some of them have answers before others close them). Those questions are equivalent of hard question which do not gets answer on SE.
Wide spectrum of users(different about the same question) also helps to close questions for different reasons, as interpretation of question depends on field of knowledge of person who votes to close. As result we get more generally acceptable questions, by WB user base.
But when Q gets more specific, significant variation, sometimes mistakes are happening, as for my opinion. As an example How quickly could modern humans go through the techtree? [duplicate] closed as duplicate, and it looks like error of some user who proposed for OP to close it as duplicate, and inexperienced user agree with it.
I personally do not see why are those two questions duplicate, for me they are significantly different questions, but for someone they are obviously not different.
In general everything works fine, but effectively it limits set of questions which could be asked on WB to Q people willing to answer.
It is rather good thing, most of the time, but sometimes Ouch happens, as reminder of existence of echochamber borders.
So in general it is more about having fun in answering question, then providing answers for reputations. And that question may have multiple answers helps there, because no policy of "first come first served no fun for others"
Point is, WB is easy on close questions(just the must thing to do, if WB do not like to turn in to a trash can) and WB like the questions it likes to answer.
how can we continue this trend in the future
More fun, do not hurry to close broad and opinion based questions if they generate content. It is a fun place until there is fun here. Fun attracts users, but do it attracts search engine traffic. (I know one question "mine jupiter" and google gives result on first page, so I guess funny question generate traffic)
, and how could we be a model for other Stack Exchange sites?
alas, no way. WB do not fits in SE paradigm, and is successful because it is impossible to strictly follow that SE paradigm for mod users(because of variety of reasons, one of which not strictly defined criteria for Q and A).