Though, you are definitely misperception. Yes, most of the people are trying hard to earn merit by posting such "consecutive or quality posts" in many boards but I don't think if you just posting quality posts could gives you merit.

As per my conclusion, people send merits mostly because someone post is actually good to deserve merits and had a lot of contribute to the forum, so, posting such "consecutive or quality posts" doesn't deserve merit even if you had a perfect grammar but it has zero meaning toward your post.