It was introduced because back during Phase 3 of the Beta test last year stupid people were spamming the Beta forum with useless threads and posts, and hence SE decided to bring some order to the chaos the best way was to implement posting restrictions. It should also be noted the Community team who moderates this forum also have to moderate the FFXI forum as well, so they're responsible for two separate forums. Really, the restrictions aren't too bad, as they're easy enough to deal with.