A menu != nav.
Menus are for application-like controls (think of a desktop app), and a nav is for navigation.
This is true even for dropdown lists, as the top-level link for a submenu often acts as a discrete link, not just a menu button. The UI may look the same, but the UX is different as the taborder in a nav should be 'flat', featuring the top-level link the same as sub-menu links.