In one of the mock exams,If I remember properly its in the first mock exam of jiris.com and also in the following link http://e-docs.bea.com/wls/docs70/webapp/web_xml.html it is mentioned tht url-pattern is optional.
Plz have a look at Writing Web Application Deployment Descriptor . It says : The deployment descriptor web.xml is defined by the Servlet 2.3 specification from Sun Microsystems. This deployment descriptor can be used to deploy a Web Application on any J2EE-compliant application server.