Comment by deepsun

Remember jabber/xmpp? At least they tried to interoperate. Google Talk at the beginning had interoperability as its main feature, but Google quickly scrapped that.

UPDATE: some say that's because XMPP was too encompassing of a standard (if a format allows to do too much it loses usefulness, like saying that binary files format can store anything). IMO that's not the reason, they could just support they own subset. They scrapped interoperability for competition only IMO.