You can only inject EJB into objects that are managed by the container(other EJBs, servlets, ...).
The "mappedBy" attribute tells the container what name the EJB should have at deploy time.
The EJB3 simplified spec does require injection to be available in remote clients eg section 4.2
The local or remote client of a session bean acquires a reference to a session bean business interface through one of the dependency injection or lookup mechanisms described in Chapter 8.
The specs also talk about 'Application Client Containers' which are supplied by some implementations to execute client applications contained in ear files. As I understand Jboss does not include a specific container and clients are built as a normal application. I see no reason why Jboss cannot support injection in remote clients as required by the spec.