i think the tomcat is a web server,and jboss is a application server,and in a distributed environment,the webserver and the appserver are seperated,you can install the tomcat in webserver,jboss in appserver.even if you host the web and app server in the same server,you still don't need to bind them together too,who can tell me what is the benefits to bind the them together?
Simply, performance is better when they are together (same JVM). You don't invoke the network overhead (RMI) through invoking remote objects.
In fact what we do is run them separately in development so that we can hot deploy to both tomcat (reloadable="true") and jboss without jarring/earring (ant is nice but I am *really* impatient during dev). So for development I find it faster to leave them separate, even if they are on the same machine.
In staging/production we us the "tied-together" version, and performance is pretty better.