I think you want: cxf-tools-wsdlto-core.jar
Right, that's indeed the jar with the WSDLToJava class and is pulled/included in jbossws-cxf.
On the reasons for using that, I think they rely on the fact that that class is able to report the version to users (it's part of the wsdl2java tooling).
Thanks guys. That's what I needed.