Hi. We got raided for this, so it's best to clear up some confusion.
No, the "3 posts per day" thing is not "3 replies per day". There is a pretty big difference, and quite frankly, I'm surprised you didn't see it immediately.
The reason this rule exists is because allowing more posts has lead to clogging the Discussions of low-quality content, and because there isn't a need for a high post count in the first place, seeing as there is a ban on off-topic posts and the game gets an update every year at best.
Users are encouraged to edit their own posts if they need to post more. They are also encouraged to use Message Walls to discuss with each other about more private/off-topic matters.