I think its a smart move to avoid low quality posters from spamming their way up to their desired rank and it reduces the work of moderators in deleting useless posts, a task that is definitely time consuming. The merit system really justifies those who are usually taking their time to construct high quality posts, worthy of moving up to the next rank though for me, the merit system really is difficult because of the fact that ranking up will rely on those who will give you merits.