Remarks
It probably seems a lot of work—just to avoid manually copying one stub file from the server to the client.
But this facility for dynamically down-loading class files has more far-reaching implications.
It is applicable not only to stubs, but any object passed through a remote method call, where the class of the actual object received is a specialization (subclass or implementation class) of the type declared in the remote interface.
One can argue this kind of polymorphism is at the heart of object-oriented programming. In this sense dynamic class loading is a prerequisite for doing true object-oriented programming with remote objects.