That is not the point. Marking a thread as solved is good, but closing is not a good idea.
We feel that a user should be able to mark his/her own thread as "SOLVED" and have it closed if he/she is satisfied with the solutions given at any point in time? They can of course reopen their thread if needed, as you've already found out.
I wrote the main reason in my first post:
Sometimes a novice can't actually assess whether a solution is good or not due to the lack of knowledge. For instance, a user asks why he can't write to the root folder as a normal user and someone suggests to run chmod -R 777 /. The asking user would say “Wow, thank you,” and close the thread, deterring other more experienced users from warning him that this is probably not a good idea at all.
It is actually the other way round. It's not mainly about other users who search for help and would need additional information (also, but not only), it is first of all for the user who opened the thread. Particularly novices can't always decide whether a solution is good. When they close their thread, no other user can correct wrong or even dangerous solutions. In the end other people coming from Google would see this wrong solution and adapt it. So not only the thread opener has a bad solution for his problem, but probably many other users too.
Nothing is preventing another user from opening their own thread if they need more help than was given in someone else's thread, so again nothing is lost.
Take a thread like this: http://www.linuxforums.org/forum/pro...t-2-lines.html
If the user had closed it, I would've never been able to post a solution that is better than this odd one he used. I don't know whether he actually read that, but in my experience, many users read answers for their threads even if they think, a good solution has already been given. But if they are able to close their threads, they would of course never come back, since no one is able to answer anymore. And other users coming from search engines would not see a better way of getting things done.
In the forum where I am moderator, we also use the "mark solved" plugin (or a comparable one), but threads are not closed when the user marks them solved. That works pretty well. Users don't cut discussions and other people like you, who don't like reading threads, which are marked as solved but still continue, don't have to read those threads. If you see that a thread is marked as solved, it is very likely, that an adequate solution has already been posted, so you can omit that one. But other people, who have a better solution or even a warning if a posted solution is dangerous, have the chance to warn the TO and of course all other people who read this thread later.
I personally dislike coming across threads that are marked "solved" by the OP in other forums, but apparently everyone else thinks they are never solved and the thread seems to continue on forever, but that's just me. Either way, you'll see a change in the way the "SOLVED" plugin works should we decide to change things.