I know we don't have access to the OSX code in its entirety, but could one argue that they actually did change how init works in FreeBSD? And perhaps that is one of the reasons the OS is stable? It's not far to assume that the Linux folks are going for more control over init for specifically this reason.
They did change init, but it is not about stability, the main reason was support of hotplug and dynamically adding and removing services. You expect stuff to happen if you plug in a new device and so on, and that is integrated into "init", so it is not so much "init" as an ongoing service that deals with events as they happen.
