Google Talk, in its current state, is hardly something I would expect from the Google stables. While openness is always welcome, GTalk hardly has anything special in terms of features. Trying to connect the various dots, here is what I perceive to be Google Talk's real purpose:
Google Talk is not really meant for the desktop. Google recently acquired Android, a start-up developing applications for smart-phones. I suspect GTalk will eventually be released as an application for mobiles rather than for desktop. With Google's purchase of dark cable, I would suspect it won't be too hard for them to blanket a city with Wi-Fi hotspots and provide Internet connectivity.
Imagine how cool it would be if you could carry a mobile loaded with GTalk, and use these Wi-Fi hotspots to call your friends all over the world.