Almost every time we answer a question and click "comment and close" it is inevitably reopened when the person that asked the question replies with "thanks!" (or something along those lines.) Then it goes back into our open discussions list even though we already read the entire response in the email notification and it requires no further action. Then we have to browse to the discussion and click the hidden link (not button...) to close it again. Micromanagement. Actually at first glance it looks like anyone on the internet can reopen a discussion again and again this way...

Github's Issues functionality gets this right: If the issue was closed people can still comment on it, email notifications still fire, etc and then if it turns out that there really is still a problem, then an admin (or support staff or "project owner") can re-open it.
Here is an example of that flow in action: https://github.com/visionmedia/mocha/issues/216

I think that's a much better workflow in most cases.