The top row of the screen - ie scriv menus and operating sys widgets goes when you use the top right window expand button - only comes back when you mouse over -
should be controlled in the scriv preferences option tick box- but this has no effect at all that i can see.
Mountain Lion user.
It can’t be controlled in the preferences because there is no control over this on OS X. The whole point of full screen is to hide those things - that’s what full screen does, expands the window and gets rid of the Dock and menu. It would go against the Mac full screen UI to show those things.
The Scrivener preference controls whether or not Scrivener’s main toolbar–the row of icons/text at the top of the project window–is hidden or not by default. If you want to keep the menu bar, try just zooming the project window to fit the screen and saving that as a layout (Window > Layouts > Manage Layouts) so you can switch to it easily–save your normal, non-maxed version, too.