Comment 3 for bug 120733

Yes, because there's enough space. It's like making a submenu with only one option inside. Why make the user click twice for something as commonly used as this?

See the GNOME Human Interface Guidelines for similar sentiment:

http://developer.gnome.org/projects/gup/hig/2.0/menus-types.html#menu-type-submenu

Guidelines
 * Use submenus sparingly, as they are physically difficult to navigate and make it harder to find and reach the items they contain.
 * Do not create submenus with fewer than three items, unless the items are added dynamically (for example the File->New Tab submenu in gnome-terminal).
 * Do not nest submenus within submenus. More than two levels of hierarchy are difficult to memorize and navigate.

There are four items, so it's a borderline case, but I think it should not be a submenu.