I get what you're saying. It's interesting that there's a different mindset since they're relatively the same, perhaps the explicit nature of action of inputting an email address is the important piece. Of course Facebook also has options for "Friends of friends" to be able to view posts, and likewise any of those friends (or people you send an email to) can forward the email or a post - or even make it public in part or whole; that explicit action of taking the effort to define who you're sending it to also likely makes receiving the message/post more valuable to the reader. The ability to CC and BCC in email also has some unwritten rules as to the intent of if you're attached as a recipient of either - ability to dictate to show others "you're the main person I'm sending this to", "see who else I've sent this to", "I want you to see this but the others don't need to know that."

Thanks for responding.