I have 1,000,000 posts and 99% of them are me complaining that other people's posts are either in the wrong place and/or have already been discussed! NO ONE WANTS TO HEAR YOUR COUNTER-PRODUCTIVE BLABBER. Perhaps instead of wasting space and memory on the GTPlanet servers with your post you can say it out loud to yourself as many times as you want...
I understand the frustration that comes with the repeated "corrections" by GTP members in various threads. "Not the right section", "has been covered before", you name it. And yet, there is a point to that.
People use GTP not only as a discussion forum, but also for getting information on Gran Turismo, currently #5. And because there is so much going on in this forum, the information may be hard to find. To improve this, there is a range of subforums which divide the GT5 main forum into several divisions. Now, when someone looks for a specific information, he obviously looks for it in the section which covers the subject. If the thread that would help him was not opened in that section however, he will have a very hard time finding it. Thus, it is important to put the discussions into the section they belong.
As for duplicate threads, this can get very nasty. I've had a couple of parallel discussions in very similar threads in my time on GTP, and it makes things very complicated and tiring. You basically discuss the same topic twice with different people, so naturally you start to cross-reference and cross-post stuff between the threads. There is very little point to that, and it also is incredibly hard to follow for an outside person. Therefore, duplicate threads often are getting closed quickly.
Now, you have a good point in saying that instead of posting the aforementioned things in the threads, people should just report it to the staff instead. In that, you are absolutely correct.