I think the big differences here are that it's a third party scanning the IP address (though possibly one Facebook hired for security scanning, as someone else below guessed), but also that Skype chat was still being vaguely claimed as "secure" at the time, I believe. Facebook is up front about scanning chat messages for spam and they do the page screenshot thing.

@kefs: I can't agree more. Here is it with Skype chats- https://defuse.ca/microsoft-reads-your-skype-messages.htm