I can't remember where I saw it but supposedly a small percentage of forum members, say 5% make 90% of the posts. 20% make 8% and the remainder make up the last 2%. Therefore, the people who post the most are going to be the most memorable while the people who never post aren't going to have any board recognition at all.
For a point of reference, about 25% of users have made no posts and another 25% have made one post. Only about 10% of users have made 30 posts to reach the "macrumors member" status.