It's worth noting that OSX does provide VNC support, transparently, as "Screen Sharing". AIUI this should be compatible with other desktop machines that run a VNC server and Bonjour.
While I wouldn't want to defend Apple's decision to drop X11 support, I should note that X11 is a minority pursuit on that platform, the Apple X11 server never worked brilliantly (Apple's use of the Alt/Meta key mapping for accented characters made for a messy collision with X11 world), and if there's a more seamless screen sharing system built into the OS, why not go with the path of least resistance?
X11 has little to with screen sharing. They always describe it as the networked window server, but in reality on OSX, it is the software that allows Inkscape and similar programs to run on your own machine.
While I wouldn't want to defend Apple's decision to drop X11 support, I should note that X11 is a minority pursuit on that platform, the Apple X11 server never worked brilliantly (Apple's use of the Alt/Meta key mapping for accented characters made for a messy collision with X11 world), and if there's a more seamless screen sharing system built into the OS, why not go with the path of least resistance?