With the difference being that nobody had a copy of your letters, just the recipient.

Not to sound like an ahole but I presume Twitter would argue it's __their__ message (in the sense that it's on their platform). with the sender and recipient having access to it. Once you hit submit you've forfeited "direct ownership" of the message.

AIM (AOL Instant Messenger) had a similar policy, which, I think, if I remember correctly, was a defining moment for AIM, and once again, for AOL.

The EULA for AIM was such that your messages became AOL’s intellectual property. Not only that you could not sue AOL Time Warner for possibly scripting and producing a movie and thus profiting from one of your instant message conversations or chat transcripts, but that maybe they could sue you for trying to do the same, and win.

I had this feeling, the moment that showed up in the news, that AOL’s days were numbered, and I was right. Other companies soon released chat functions, including Google and Facebook, and now AIM is gone. It was a signal that AIM was unsuitable for enterprise messaging, and no one excpet teenagers should bother with it, and wventually the teenagers that did use it, grew out of it, and moved on, and the rest is history.