Some of us choose native program over Web app for a reason and I believe there are many like me would stick with it.
You should also probably realize the point of using XMPP is that it's an open standard, and anyone is allowed to make their own implementation; contrast with the uneasy interoperability of, say, MSN Messenger with Pidgin. Now they're using Jingle, do you need a first-party client? You don't expect first-party SSH clients from your hosting provider, or first-party email clients from your ISP. And god knows there are enough IM/VoIP clients out there, so I'm all for thinning the herd...
Well there is always http://talkgadget.google.com/talkgadget/client
Opening a webbrowser window with that and you are set. No Gmail UI, and you get video chat.