I also frequently run into the situation where I Google something, there is a perfect match on a SO question, but then the answer is "Actually, you don't want to do that thing you asked about, here is a different solution for your specific scenario". But often that alternative solution is not relevant in the general case, and there really are good reasons to want to do the thing as originally asked in the question.

Basically there are all kinds of situations where the specific question/answer format is actually at odds with generating good long-term documentation.

But that makes me all the more impressed with the success Stack Overflow has had. In my opinion their key insight is that it can be good enough. If I had come up with the idea for the product I probably would have been discouraged and given up way too early based on the fact that it is and will always be messy and imperfect.