Actually, the post count is over 28400 (this particular post is the 28409th). It's just that the actual post count doesn't include the deleted posts. The database ignores the deleted posts so that you don't get two posts of the same number. It's complicated to explain, easy to understand.
If you understood this, get yourself a cookie:
Basically, if the actual post count (ie, the number of posts in the database) is 15 and post number 14 is deleted, the next post will still be post number 16 according to the database. If that didn't happen, you'd end up with two 15th posts because the database won't think to move the original 15th post down so that it's 14th. Why? Because it would slow the forums down completely. The number of posts will still be 15 but the database will read the count as being 16.
I'm good at noticing that sort of thing.
Sorry to kill all your vibes.....not.