It's more work to write a client library for XML-RPC/SOAP, but a single one of those libraries is likely to work with any such service you encounter. Most users never have to write one themselves.<p>On the other hand, it's easy to write an HTTP "REST" client library. But it seems that everyone has a different idea of what REST is. Amazon's implementation of REST isn't even close to the generally-accepted definition, for instance. Indeed, you need (to write) a separate client module for every service you use, and that's where REST fails.<p>Because it's so easy to write a REST service, it seems more like REST is an excuse for lazy server writers to get by.