>Does anyone even use full-screen apps?
Yes... on laptops. This is something I've observed watching my own customers work with software -- on desktop machines, few things are truly maximized. On laptops, nearly everything is maximized. I think it has to do with screen real estate. The more you have, the less likely you are to want to fill the whole thing with one window.
Making the green button work to maximize is probably the right choice for the smaller devices. If they want a consistent UI across all devices, that's the right call given the prevalence of smaller devices.
It makes the behavior match MS Windows... I doubt Apple considered this a plus, but I work back and forth across both OSes regularly, and that's one of the few kinks that has caught me.
> At least Apple should put a toggle in system preferences so the user can revert the behavior.
Yes, that would be nice. I agree. But that is explicitly what Apple does not do and what they generally consider to be A Bad Idea. Such toggles lead to low-use code paths in the OS, which means they don't get nearly the same amount of testing and they increase the complexity of the underlying software, increasing the risk of bugs in both settings. I've encountered that philosophy in many companies with large scale software -- better to leave out the option and give people something that you know works rather than put in the option and increase your bug risk.
Question: Does anyone know of actual studies done to demonstrate validity of such philosophy? I've heard it described many times, but I don't think I've ever heard any research into it.