Why do I need additional configuration in JBoss EAP to access the MBeans from a JMX Client?

Issue

With the Eclipse "MBean explorer Plugin", service:jmx:rmi:///jndi/rmi://node2:1799/jmxrmi, results in the following error message

"An error occurred while opening the connection.
Failed to retrieve RMIServer stub: javax.naming.CommunicationException [Root exception is java.rmi.ConnectIOException: non-JRMP server at remote endpoint]".

The plugin website http://code.google.com/p/eclipse-jmx/wiki/HowtoUse states I must use the following start options for the VM to start an Agent :

-Djavax.management.builder.initial=org.jboss.system.server.jmx.MBeanServerBuilderImpl -Djboss.platform.mbeanserver 
-Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=3000 Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false

After changing the configuration, I see the MBean-Tree, it works with service:jmx:rmi:///jndi/rmi://node2:3000/jmxrmi .

• Why can't I fetch the MBean-Tree with the direct access over the JBoss-Jndi without the agent ?
• Why do I need additional configuration in JBoss EAP to access the MBeans
• What do the jmx agent configuration parameters mean?
• We have enabled the remote jmx, However we are not able to access the mbeans.