I notice that some questions have lots of good answers, but there is no accepted one because some people come to StackExchange expecting answers right away, but leave after they see that nobody is responding. These questions become popular spam places (well, not exactly spam, just repeated information) for new users. There should be some kind of functionality where moderators, trusted users, or even the site itself can manually award it to someone or to the highest voted answer.
This has been discussed several times (in the meta of metas), and declined the same amount of times.
This gets brought up from time to time on MSO and the response is generally not favorable. I wouldn't hold my breath, personally.
The system considers a question "answered" when it has at least one answer with a positive (non-zero) score.