I've been using a definition for RIA since I first wrote about as an independent analyst for Burton Group in 1995.

A RIA is:

(a) Browser bound; executes inside a browser
(b) Is programmable by developers
(c) Provides the ability to do network communications with remote nodes
(d) Focuses on providing a framework for GUI.

This eliminates something like an audio player or Quicktime but includes programmable platforms like Flash/Flex, Silverlight, Ajax, Mozilla XULrunner (or whatever its called) and Curl browser applets.

It also, because applications are not bound to the browser, eliminates Adobe AIR and Curl desktop applets and applications. These platforms, which grew out of RIA technologies, are "Fit Clients" or something else.

Microsoft has a history of not adopting terms used by other vendors. For example, Microsoft uses "Software and Services" rather than "Software as a Service" (SaaS), or not using SOA, or using "Mesh" instead of "Cloud". That's nothing new and I don't fault them for it - their avoidance of SOA as a terms seems pretty smart to me. That said, I think Rich Clint Platform is more confusing than enlightening. Does that include Flash? What about WPF? Is Java SE (not the browser plugin) a RCP?