Dev here, happy to answer any questions!
If I used facebook's XMPP interface, I could do real-time chat in the chat head. But facebook's XMPP interface doesn't allow for group chat or offline chat.
There are plenty of facebook chat clients, but none of them do group chat or offline chat, so I decided that was more important than real-time chat in the chat head.
Hope that addresses your concern, if you have any suggestions I'd be very grateful to hear them!