On the other hand, that very separation is X's greatest hindrance. It imposes a fairly large cost, not just in terms of performance, but also in terms of complexity. You have to deal with a network protocol just to display things on the screen. No other windowing system imposes this level of cost on the developer, and it can be argued that the reason we never got a Linux desktop was because of X. Simply put, Apple showed us what could be done with a Unix system if you abandon X and set allow your GUI API to talk directly to the hardware. A large part of Apple's success can be tied directly to their decision to forego X11.