Mark Baker has a theory as to why there are so many interop issues with some pretty basic stuff in the WS* world - it all boils down to the ease of testing:

What I think this boils down to is that interoperability testing of Web based services (not Web services), like any Web deployment, benefits from network effects not available with Web services, primarily due to the use of the uniform interface. So if we're testing out Web based services, and I write a test client, then that client can be used - as-is - to test all services. You simply don't get this with Web services, at least past the point where you get the equivalent of the "unknown operation" fault. As a result, there's a whole lot more testing going on, which should intuitively mean better interop.