I'd echo SteveandViv's comments. They probably just mean a proper 4wd. Ie, something with a low-range transfer case or lockable centre diff, and decent underbody clearance. Without starting a fight, that's the usual line-in-the-sand.
You'll also see signs out in the bush saying things to the effect of "Suitable for high-clearance 4WDs only" - generally this just means the same as above, a "proper" 4WD. IE, technically I have 2 x 4WDs, the Pathfinder (play nice now people
), and the Subaru Impreza. The above sign tells me that I probably shouldn't be taking the Impretzel down said track (but I'd be tempted to give it a shot).
A current model triton would certainly fit the category of High Clearance 4WD, as to "Heavy Duty 4WD", as Troy has alluded to, it's a bit open ended, but I'd be tempted to give it a go. Again, as Steve says I'd probably be wanting to invest in a set of good tyres (AT's at least, in a LT construction for strength) for peace of mind, and maybe a bullbar for approach angle clearance, but careful driving would get around that.
Don't worry about the Trackabout - you're unlikely to be able to get the Triton anywhere that will phase the camper. That's the main reason we bought one!
Clear as mud?
Thanks!
Matto