Well, that is a protocol comparison. A client comparison would be much closer to the real world user experience. Don't get me wrong, I am a huge fan (and daily user) of XMPP, but the best protocol will not be of any use if the clients are too complicated or buggy to use.

So yes, XMPP supports audio and video calls but finding two different clients which work on the first try together can be a challenge. Sometimes I wish there would be some compatibility XEP which defines a common set of supported XEPs including a test suite to run it against.