This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates 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.