Dick, I'm not sure the situation is much different anywhere else.
In the USA, there is a myriad of military areas, including Restricted Areas, MOAs and Warning Areas. The control zones around the associated airports are small, but the adjacent areas are often large (particularly for fighter and warship ops). File any route you like, but be assured of an amended route if planned through any of these areas during published hours. Once airborne, the controller may clear you more direct on their own initiative or on pilot request as long as the airspace is released by the military.
Related, is a recent initiative in the USA to have pilots plan more diligently, because the re-routes are handled manually, adding to controller workload. That program is called File Smart, and it's basically a voluntary program to reduce controller workload. In Australia, a system of mandatory flight planning routes are published to achieve the same end.
My understanding of Williamtown is that you have to plan via the approved route, but can request more direct airborne. In the case of MDX, the clearance was available (the pilot did not know that when he made the decision to track via CRAVEN), but he elected not to wait for it – things weren't as instantaneous back then, especially if you were talking to Flight Service who had to relay from ATC, and anxiety makes every moment seem longer.
Ending up over the Barrington Tops in very rough weather on limited panel is a nightmarish, if not impossible situation to handle, but IMHO it's a pretty big stretch to blame the RAAF.
Radar? I can't see how radar would help the pilot recover from a (likely) spiral dive on limited panel.