What makes a question a "real" question?
There's a blog post about this: Real Questions Have Answers. That seems pretty obvious, but not every response is an answer — and a pretty good indication of a "fake" question is one that attracts a lot of responses, but few answers. The FAQ spells this out:
You should only ask practical, answerable questions based on actual problems that you face.
Your questions should be reasonably scoped. If you can imagine an entire book that answers your question, you're asking too much.
If your motivation for asking the question is “I would like to participate in a discussion about ______”, then you should not be asking here.
So if your question starts attracting responses asking for clarification or additional information, or responses that are at best partial answers and at worst little more than opinions, chances are you haven't asked what we'd call a real question.
What are new users expected to know about asking "real" questions?
Asking a good question is hard.
If you walk over to your guru co-worker's desk and ask him a question, chances are the response won't be an answer — it'll be a request for more information, and if you don't — or can't — provide it, he'll likely tell you to come back when you can.
Stack Exchange tends to be the same way: you probably won't ask a great question the first time around, but if folks can at least understand the gist of what you're after they'll ask for clarification — if you're quick to provide it (by editing your question), then you're on your way to asking a "real" question. And next time, you'll have a better idea of what to include at the start.
If you decide to ask a question and then go to bed, well, you can't really blame anyone for deciding that maybe you didn't really need an answer.
Why does SE treat questions differently from other online forums?
Remember that guru co-worker from the previous section? Well, a traditional forum tends to be like a literal record of that entire conversation, which can be a bit tedious to follow for someone else with the same question — so the end result is that the same questions get repeated over and over again, until the guru just buys a good pair of noise-cancelling headphones and ignores you.
Oh, also all of your other co-workers tend to be standing around, kibitzing. And now and then someone wanders in off the street and asks for directions to Walmart or tries to get you to buy some fake designer jeans.
Point is, traditional forums tend to be noisy, which is great if you're looking for some human fellowship, but not so great if you just need an answer to your question.