Wrong reasoning. If I start a topic on the problem that I have, the moment that the problem is solved is the moment to lock down the topic. If you think that in that topic is not written enough, start new one. Making topics too long is bad thing. Search is the best way to find info that you need (if info exists).
Usually the exact opposite thing happens, many users leave the threads open and then users "reopen" that thread after 4 or 5 years of inactivity to post their own question which may be similar to the original question.
I have to add that I have seen some cases in which the thread was closed with some wrong solution, in that case you can PM the original poster.
When you PM the original poster he can reopen the thread until a correct solution is found but it is up to the OP so I guess there will be cases that a thread will remain closed with a wrong solution even after the OP is notified about the wrong solution.
Yes, that has to be accepted, if a close-my-thread feature exists. I don't think, that it's major problem. I remember a few cases, when I took part in discussion and found the thread closed overhasty, e.g. with a wrong solution, that has been gladly accepted by the original poster. On the other hand, nobody can correct all wrong or misleading solutions posted at edaboard.
Personally, I don't think that it's appropriate to close a thread unless it has a very special topic and has been answered exhaustively. It's also O.K. to close a thread, that has been mainly based on wrong assumptions. In other cases, I tend to leave an option to carry it on in follow-up posts. As already mentioned, there are many cases where newcomers are adding unrelated comments or retelling previous posts. But this bad habit isn't a sufficient resaon to close all threads.
I too disagree with the closing of threads just because the OP has had the reply they wanted.
Many times someone else can come along and find a topic that they are interested in yet may not have all the information they need so simply asking an additional question or making a further comment can improve the thread.
Also, many times when someone comes on the board and asks a question they get told to "do a search first", to find an existing thread on the subject.
But if that thread is locked then they end up making a new one anyway.
By all means have the [solved] tag, but not close it.