I looked at the spec and referring to page 395, what i understand is that the "implementation" classes of the Handle and HomeHandle interface must provide those methods. The writeObject/readObject methods of Handle/HomeHandle interface implementation class must call the HandleDelegate methods to perform serialization/deserialization of the handles. Also,
javax.ejb.spi.HandleDelegate service provider interface is not used by enterprise beans or J2EE application components directly.
Since these methods are in the implementation class and not used by the enterprise beans or applications directly, they have not been shown in the interface.