My desktop behaves in this way (three shutdown options: Stand by - Turn off - Restart; holding shift changes "Stand by" to "Hibernate").
So why does my laptop have four shutdown options always visible (Hibernate - Stand by - Turn off - Restart)?
Both the laptop (Dell Inspiron 9300) and desktop (Dell Dimension 8400) have Windows XP home edition, service pack 2, enabled hibernation, and (as far as I know) all the same updates/patches/hotfixes.