On Laura Thomson's blog, there's this post that talks a bit about XML and web services.

In a nutshell: most of the web services stack is bloatware that doesn't get used for most applications. 90% of the time you can get away with knowing no SOAP, WSDL, or any of that stuff. You can just use REST - Representational State Transfer. This is basically an HTTP GET request with parameters, and in return you get an XML document, in other words XML over HTTP. It works very nicely and is simple.

She gives a basic example of how, using nothing more than SimpleXML in PHP5, you can create a client/server with REST to communicated back and forth.

I'm not saying there isn't a need for SOAP and WS-*, just that often simple tools will do the job. It's just another version of the 80% rule. This seems to be a theme in my personal consumption of technology.