These companies blame the GST when it's their own greed that causes people to shop elsewhere. They don't even have the bricks-and-mortar excuse, because Australian online retailers are just as big thieves as their bricks-and-mortar counterparts.
Example: I can buy a 16 MP digital camera with 24 x optical zoom for $260 from a Chinese drop-shipping site. The cheapest similar camera from an Australian online store is $430. That's a 165% markup. GST is 10%. If it was applied to me buying the camera from the drop-shipping site that would mean the camera costs me $260 + $26 = $286. Still a damn sight less than I'd be paying to an Australian retailer.
So even if the government bows to the retailers and makes us pay tax on online purchases it still isn't going to stop anyone from buying from overseas retailers.
Finally, these companies are the very same ones who were quite happy to outsource Australian jobs to cheap third-world labour. How dare they complain when we, the consumers, do exactly the same thing by outsourcing the purchasing of our products! Hypocrisy much?