Marketing. So many people buy based on the label (design and reputation and not necessarily in that order). The design options are starting to run out on the limited area of labels, so now the bottles are changing shape and colour to make them stand out in the plethora of options in the bottleshops.
Australian wines attract a huge premium in their home country. And state-by-state, the premium goes up. I live adjacent to the Yarra Valley in Victoria where Moet & Chandon has a vineyard along with some other fancy wineries. I looked through some local bottle shops the past week or so, and the starting prices were AUD$13 and went upward from there, and averaged, I think, about $20.
Having experienced Tasmanian wines and their inflated prices for not much better quality, I have somewhat lowered my palate's desire for marketing hype . I now go for light red wines such as roses and a new white shiraz (still a light red) and am very happy with their tastes and after-effects. I figure $6 or $7 a bottle is about my usual limit, although I still will spend $13 on a bottle of the good old reliable Portugese Mateus Rose (which is not a fashionable wine at all now, despite it being around since Adam played full back for the Pythons -- but then, I'm not much into fashion these days).
I'd suggest that at the price you paid for the shiraz and because it has impressed you so much, you go back and buy a case or two.