Wait, these are the messages that are sent between two users? Does just one of them need to put their settings on "Everyone" to display both sides of the conversation?
Please tell me this is a bug/hack/exploit/mistake/error.
That makes more sense. Wall posts are meant to be public and apparently these people love to over-share.
What do the settings need to be in this situation? The recipient needs to have their wall set to "Everyone" and the poster needs to have their wall postings set to "Everyone"?