Tom, it all depends on your usage scenario. Do you use it with default (demo) setup or you have your custom application that does the interaction with the engine?
Updating WAR is due to jbpm-console server component is responsible for executing your processes, so it must be able to find it on classpath to register your custom work item handles onto the session and of course to find the class of the work item implementation. When you use your custom application it is up to you to either rely on discovery mechanism (same as jbpm-console) or do it manually when creating a session.
HTH