I was asked to co-author a white paper on the state of rich clients in this "Web 2.0" world. As I thought about it, "rich client" doesn't seem an appropriate term for the state of the art interfaces of today.
Rich clients were developed to inherit some of the server's processing responsibilities and lessen network traffic. The idea was to distribute the application architecture in the direction of the user to preserve server resources and bandwidth. What's happened in this service-oriented and large-piped world, is that the architecture has been distributed radially. Now, servers become repositories for small and discreet bits of functionality and content. In addition, if someone else is already providing a particular service (say, geocoding), you don't even need the infrastructure to support it. The best clients today are merely aggregators of service-oriented and syndicated information or services.
It seems to me that a better term for these interfaces would be "thick skins." Thick skins are ways of collecting various "feeds" of content and function in one interface.