EJB is a popular architecture for building web applications, but it suffers from one significant liability: EJBs are accessible only from Java applications. While it is possible to use some arcane CORBA techniques in conjunction with RMI/IIOP to get to EJBs from non-Java programs, it is rarely worth the trouble. However, EJBs often expose functionality that you may want to make available to non-Java clients.
The next chapter shows how to build web services that are accessible by other, non-Java, systems, including Apple's proprietary scripting language, AppleScript. This lesson will round out your enterprise development skills on Mac OS X, and probably make you all the rage at the water cooler as well.