I just now tried it and it worked fine for me, both when starting JBoss AS from a command line, and when starting it within Eclipse. In both cases I eneter http://localhost:8180/admin-console in a browser. So I suspect that there is something else going on in your situation.
By the way, changing server.xml is not the recommended way to change port. See http://community.jboss.org/wiki/AS5ServiceBindingManager