The more I think about this, and read about it, e.g. here, or here, or think about it in this context, the more firmly I believe that Java, or any strongly typed programming language, is not a good vehicle for building document-oriented Web services. If you contrast the standard Java APIs for SOAP (yes, I know Web services and SOAP are not equal, but anyway), it's obvious that JAXM, while a lot more flexible than JAX-RPC, is also extremely tedious to program. If you compare this to e.g. Aaron Swartz's xmltramp, Sam Ruby's lazydom (both for Python), or Doug Purdy's Smalltalk solution, they combine the usability and elegance of accessing elements directly with the dynamics of not tightly coupling your code to a specific version of a document format.
My prediction is that either Java will somehow enable this, or be to Web services what C is to OO.