If you ask me, the system should have an Accepted Answer review process. Several possible suggestions follow.
Community Accepted vs. Poster Accepted
Allow two "accepted" answers: one by the original poster, and one by the community, which can be set, cleared, or changed by a formal review process requiring X votes. Periodically, as technology changes, one answer is often invalidated and a new answer should take its place. Unfortunately, under the current system, it's not possible to suggest this except by comments, and answers that are accepted are protected. The community at large should be able to influence this instead of placing the burden on the original poster. The community accepted mark does not bear any associated rep points, but helps guide visitors to the correct answer.
Unaccepted or Incorrect Answer Review Process
Allow the community to set, clear, or change the accepted answer by a review. Flag the answer that should be correct and allow the community to review it into acceptance. To reduce the odds of abuse, answers set, cleared, or changed in this manner don't modify the rep of the original or new answer owners. It would be really cool if "Community" (the automated user) could periodically randomly choose questions and answers for review so that reviewers can determine if the answers are still (probably) valid as well or if an accepted answer should be set.
Flag to Prompt Original Poster
Instead of leaving comments, allow the answer to be flagged as a possible accepted answer. If the review passes, send a message to the original poster's comment feed prompting them to select an answer. Of course, this still leaves burden on the original poster to do the right thing, but it avoids the hassle of comments. Under this option, the original poster can choose to accept or deny the answer (perhaps because it didn't answer their question satisfactorily, etc), but if they do nothing in a reasonable time period (perhaps because they've never logged back in, etc), consider marking the answer as accepted.
Free for All
A question and answer that's been abandoned (neither have been touched in at least 30 days or so) will be flagged for review automatically, and the community can choose the correct answer through the review process. Alternatively, once the abandoned state has occurred, anyone with sufficient rep can set, clear, or change the accepted flag. No rep changes will occur to the original or new answer owners as a result of this change.
I'd be okay with any of these solutions, or any other similar solutions that allow the community to ping the original poster privately and/or allow a consensus among trusted users or a vote by moderators.