That's because the JMX interface is not meant to replicate what cache interface offers. It's meant for monitoring and management.
Instead, either start the cache programatically and pass around Cache references, or bind CacheManager to local JNDI and then retrieve a Cache from it. Sample code on binding a cache manager to local JNDI can be found in http://anonsvn.jboss.org/repos/jbossas/projects/cluster/ha-server-cache-jbc/trunk/src/main/java/org/jboss/ha/cachemanager/CacheManager.java