Except you don't have to browse to page four of a giant thread to find out a posted solution doesn't work, and you can update an old answer when the information becomes outdated, etc.
Again, though, you're missing the point. On StackOverflow, a stale answer can be fixed, by virtually anyone. On traditional vBulletin-style forums, the post saying "this isn't true anymore, there's a better way" might be buried hundreds of posts in.
I often land on a question that I'm asking, and it has a lot of upvotes, but it was answered 3 years ago using deprecated APIs.