Exactly, Lucid. *nods*
The posts/day is an average of your total posts divided by the number of days you've been a member. It's not that you actually post x per day, but that if you were to post a similar amount per day, you would be posting about x per day on average. This takes into account days that you post a billion times as well as days you didn't post at all. It's not that confusing. xD