WebRPC is a lot lighter than XML-RPC (or JSON-RPC). It's really just a thin layer on top of HTTP. Arguments are passed in the query string (or as form parameters, if POSTing), and the response value is returned directly as JSON. There's no body or envelope to parse. This makes WebRPC services really easy to consume by any client that supports HTTP and JSON (which is pretty much most platforms). WebRPC services are also really easy to test, since you can execute a method and get the results back simply by typing a URL in your browser.