total diskspace is not calculated from the database really.
I mean statistics has two figured in admin one is from database and is merely a cumlative total of the filesize field in the photos table. That is the main image. You have to take into account diskspace is what is on the actual server and contains all images thumbnails mediums and large images and uses the php dirsize function in the actual code not a database call.
classifieds stats are indeed in the database in the stats table
reviewpost views are most definately in the database products table under views field.