OH! I get it now. When you see a post from me, you'll see all my comments AND all the discussions I've started (17). However, on my profile page, they break those two down. 17 discussions and now 12,001 comments.
It would seem like that they would had included the posts made to the Activity Feed to be included in our total posts but my guess is that they didn't do it like that as they wanted new members to engage in the forum sections to get those counts up instead of spamming the Activity Feed. I have seen some New Members doing just that with the Activity Feed thinking that this is the best way to get their post count up instead of posting in the forums