The feature is still draft and only made version 1 in June 2009 (http://xmpp.org/extensions/xep-0166.html). I don't actually track changes in XMPP so I am open to correction on this point.
Around the time I actually wrote the article (many months before it was originally published in .net magazine) there had just been a libjingle release and I was told at the time it was a new thing to have this available to 3rd party developers.
Also, GTalk does not use libjingle but its own slightly-different pre-standard implementation, that's why it is impossible to talk to GTalk users with a XMPP client that supports Jingle via libjingle.
Around the time I actually wrote the article (many months before it was originally published in .net magazine) there had just been a libjingle release and I was told at the time it was a new thing to have this available to 3rd party developers.