Editing posts is explicitly encouraged in the text reported by the FAQ:
All contributions are licensed under Creative Commons and this site is collaboratively edited, like Wikipedia. If you see something that needs improvement, click edit and help us make it so!
The reason for which improving posts is encouraged (whatever they are questions or answers) is that they need to be useful to any user that will read them, not just to who asked the question, which is the purpose of every Q&A site of the Stack Exchange sites. In fact, a question that is relevant to the user and for few other users are closed as too localized.
Answering to questions is just one of the tasks that users can do on SE sites; other tasks, such as voting to close questions, flagging answers that are not really answers, reporting spam users (or flagging the posts that are spams), reviewing the first post of new users, and editing posts that need to be improved are equally important.
You could argue that there isn't the need of closing questions either; if a question is the duplicate of another one, then once the duplicate is reported, users should answer to the duplicated question (if it doesn't have an accepted answer) and stop answering the new one. Contrary, closing a question that is duplicating another question is necessary to reduce the noise ratio; if the noise ratio is too high, then questions that are still without an answer would pass unobserved.
Only users who still don't have the privilege of editing all the posts get 2 points when their proposed edit is approved; the other users don't get any reputation gain for editing, but they are still doing a task that is considered necessary (when posts are improved). To avoid any reputation chase, proposed edits that are partial are normally rejected; it would be too easy for somebody gain 6 points by editing in 3 different occasions what could have been edited once.
I would also say that if high reputation users would be the ones that always answer to questions, other users could not gain any reputation. I much prefer that other users participate in answering the questions, and gain more reputation. I think that is the purpose of giving more privileges to users with higher reputation; in this way, they can attend other tasks that are necessary for running an SE site, and somebody else can answer to questions. With that I don't mean high reputation users should not answer anymore. I just mean that I would be worried if there were just 5 high reputation users, and the other users would have a reputation of 500; one of the criteria for verifying if a beta site can go forward is the number of users with a minimum reputation, and Drupal Answers had the sufficient number of users with the required reputation.
