Some questions will never recieve an answer, because they have been abandoned. One example is this one: 'Notify user of new account' checkbox to be selected as default The same goes for question which are not clear, commentors have asked questions, but the OP does not return to the question to clarify.
Can a moderator/high reputation member "force accept" an answer? If so, should they? I dislike leaving unanswered questions remain un-answered when there either actually is a clear answer, or never will be one.