A Time Before the SOAP vs. REST - SOAP vs. XML-RPC

With the ongoing debate about the pros and cons of SOAP as compared to REST, the scholar in me got to thinking about the last round of debate between XML-RPC vs. SOAP. (Funny as it seems now, think the first time I came across REST was this article on Creating and Consuming Web Services With PHP - REST was mentioned as a final footnote...).

In particular, it seems that no-one's much interested in arguing around XML-RPC now, although a three-way comparison does occasionally turn up, like in this consideration of Consuming Web services in PHP.

This is possibly useful and/or interesting. What is it about XML-RPC that makes it no longer a topic of interest? Has REST taken over one of the lines of argument, or have some of the arguments in favour of XML-RPC lost out to SOAP? I seem to remember that the old Amazon webservice API gave examples for SOAP, XML-RPC and then later on for REST, but their new ECS API focusses on REST and SOAP (I think...)