I found my solution.
I think the annotation did not work because of some jar conflict. Therefore I copied the "jbossws-spi.jar" to my project class path, but I did not build it into my compiled and deployed EAR. (I used an Apache Ant build script to do this.) Thus, my source code recognizes the @WebContext annotation, but the build application relies on the annotation's implementation stored in JBossWS in the server. Now I understand!
@WebContext(transportGuarantee = "CONFIDENTIAL") put my web service in HTTPS. I hope this helps others who have the same confusion.