Well, a big factor in usuage stats is whether you are allowing attachments. My board has attachements to most posts, but my bandwidth usage is relatively low. But, I don't have a very active board, and it hasn't really been used for a message board, more of a file storage management system.
But, yeah, attachments are going to raise your usuage. Of coarse, there are a few hacks around to help you control those. I would be interested to see ericgtr's stats with his attachment heavy board.
