I guess that it's ok because when you are using annotations and named queries there is not need to generate something. Named queries in annotations are completely fixed and static and they are supposed to be read only once by Jboss. If you really want to generate where expression you can always use EntityManager.createQuery.
see
http://download.oracle.com/javaee/5/api/javax/persistence/EntityManager.html
Actually I have never tried to generate where expressions for namedQueries because they should have been created before an application is deployed to an application server.