This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
Welcome to ORM land. In your first example, Hibernate "knows" what it wants and generates SQL accordingly.
In the second you are bypassing Hibernate with native SQL so it basically does what you told it.