Although, I haven't tried any realtime example by coding but I think that <jsp:root/> is not a "must" in below scenes:
1. The request path matches the URL pattern for a web.xml JSP property group declaration with an <is-xml> element set to true. See part two of this series for more on JSP property group declarations.
2. The request path extension is .jspx, unless this extension matches the URL pattern for a JSP property group declaration with an <is-xml> element set to false. In other words, .jspx is the default extension for JSP Documents, but it can be explicitly disabled by a property group declaration.
3. The request path extension is either .jsp or matches a URL pattern for a JSP property group declaration and the root element in the file is <jsp:root>.
Marcus, Pls. have your comments on this.
Please refer following link for ref. http://www.onjava.com/pub/a/onjava/2004/04/21/JSP2part3.html