According to the Fedora Wiki in Gnome 3.4 "maximized windows can gain more screen real estate by hiding their title bar."
The title bar above a maximised window has always seemed like a waste of space to me. The information it contains is redundant as the same information is visible in the panel and the address bar. Why not hide it?
In Gnome 3 the function of the close button in the title bar is duplicated in the panel icon, where the right-click options from the title bar could also surely be duplicated.