I wouldn't consider requiring a ton of mostly redundant and useless information in messages (each namespace needs a whole damn URL every time it's referenced? Does the parser use it, or even care that the entire URL is correct?) and XML parsing (which isn't so bad, in comparison to all that redundantly redundant redundancy) to be "simple" at all. WSDL/XSD is yet another layer on top of this mess of complexity and I suppose you're referring to the fact that it looks simple if everything goes according to plan, but when it doesn't it's anything but simple. Trying to get any kind of performance out of it is another counterpoint to "simplicity"... This is all from the experience of someone who has worked with XMLA-based OLAP systems.

That link you gave has a summary part ( http://www.diveintopython.net/soap_web_services/summary.html ) that says "SOAP web services are very complicated."