When a deployment or a virtual host is stopped in tomcat5, an access attempt is replied to with:
HTTP Status 503 - This application is not currently available
When a deployment is stopped in tomcat 6, it replies with 404.
When a virtual host is stopped in tomcat 6 it replies with 400 Bad Request.
Tomcat 5 behavior seems more consistent. Let me know if tomcat community has decided for such change.