Jabber rode the wave of "everything must be xml". Try debugging anything that's based on irc - you can do it using telnet (and/or tcpdump, if you need to see full client-server interactions). Now try doing the same for Jabber. Typing xml snippets into telnet is not pleasant.
Indeed, which is why it's typically not done, there are many better XMPP clients with debugging capabilities (including command-line ones) than telnet.
Personally I much prefer debugging XMPP to debugging IRC protocol issues since it's always obvious what is going on from what goes over the wire, whereas in IRC you are frequently forced to look up random specs to figure out what some obscure numeric code means to a particular implementation of the protocol.
