Speaking of Adium, they will bend over backwards to support a proprietary chat system from a huge site like Facebook, but they are not going to add support for

Speaking of Adium, they will bend over backwards to support a proprietary chat system from a huge site like Facebook, but they are not going to add support for arbitrary startup's creations. Using XMPP allows your users flexibility in how they access your service. If Adium is how they choose to stay connected, then great. Sites like Identi.ca have XMPP interfaces for precisely this reason, and it didn't take long for Twhirl and others to add support for Identi.ca since it was well documented (via XMPP standard) and easy to do.