This used to be true, but there's a feature currently in testing that will allow anyone (even someone coming from Google) to propose an edit to a post. This edit proposal can be approved either by a moderator or several users with sufficient rep. Hopefully this will make Stack Overflow more wiki-like and help solve the problem with answers getting out of date.

This sounds similar to how Discogs has implemented quality ratings (via votes) for arbitrarily edited content, in between full editorial control and open wiki.

That sounds like a great idea to me

I think thats a big problem with the "accepted answer"

Firstly it's accepted by the questioner - who by definition knows the least about the subject, otherwise they wouldn't be asking!

Even if it is correct and well written - then it stays accepted years later when it's no longer the best way to do something.

The temporal nature of best practices is my biggest complaint with how SO works. It works great for relatively static subjects, but its useless for fast moving technology targets due to the community resistance of duplicate questions.