I'm not 100% sure, but it seems to me that VOZ replaces the default ground textures of FS9, so that Australia looks better.
The drawback of this technique is that depending on the area you want to fly in Australia, you must first change the texture set to choose the one that correspond to that precise area, because the whole australia (world ?) will have those ground textures.
I think they did that because it would have been too difficult (or too long) to create a full scenery that would cover the whole continent, with it's own textures precisely attached to each particular area (like what is normally done for little sceneries like piece of airports, or cities or villages etc...)
Correct me if I am wrong.
You're absolutely right, Daube, it changes the whole world not just Australia. There's a 'switcher' programme which swaps the 4 'regions' of Australia, i.e. temperate, dry, desert and tropical, depending on where you want to fly. You can also 'unvoz' with it, of course, back to whatever textures you have. There are now most seasons available, if not all, within each region. The temperate and tropical look really good, the other too are a matter of taste - the desert is REALLY red.
It isn't a problem that it changes the rest of the world - in fact it's a bonus :) However, the colours look strange in some places, but tropical is good for much of Asia, and other tropical places, and temperate looks fine in temperate regions too. I used it for these Japan shots.