Working as designed.
Facebook and Twitter aren't designed to be understood by the users. They're designed to easily and quickly share as much "monetize-able" information about users as possible. I haven't used either, but it would seem to me that it would be trivial for the distinction between public posting and private posting to be made obvious to virtually eliminate Wenis errors like these. E.g. different screen background colors for public and private posts (like different virtual terminal colors for SU sessions). The user doesn't need to understand the technology; the people who build it need to understand their users' needs if they're really interested in protecting their information.
My $0.02.
Cheers,
Scott.
