It depends on the culture of the place, but stackexchange (like stackoverflow, superuser, etc.) sites allow users to post a question, post an answer to that question, and accept that answer as the best one (the same person doing all these). In these cases, the questions and answers act like one piece of an FAQ or a best practice to educate others. Since stackexchange sites are also inherently wikis, allowing all questions and answers to be edited by anyone (with sufficient reputation scores and reviews by others), it could help improve the quality of the content for such pieces.

I know I hate when I search for something and I find my question on a forum and then the poster responds "Nevermind, figured it out."

Oh, I know. That just makes me fume. And mostly because it reveals the very selfish nature of the poster. As if everyone on this public forum is just waiting to serve you and you don't have the time to make any useful contribution whatsoever.