My understanding of this (and please do not rely on it as I am not a tax specialist) is that the overseas seller only needs to register for collecting and paying GST, where the turnover (which means the gross sale price totals) from sales made to Australian buyers as part of their selling enterprise, is $75,000 or more per year (including shipping costs).
Therefore, if Pinball Resource works out that it sells in total sales about $50,000.00 a year into Australia with $2,000.00 in shipping costs, its GST turnover is $52,000.00, and therefore it does not have to register for GST purposes for the new rules, and therefore does not therefore collect any GST on its sales to Australia. Nothing therefore is changed if this is the case.
Amazon, which would I expect easily sell more than $75,000.00 into Australia per year, chucked a wobbly and said no. Not sure how much this was done to promote the AU version of its site (which no doubt 50% higher prices) than the reality - all it has to do is register, and sales made into Au automatically have 10% added at checkout, and this is remitted to the ATO - pretty easy, so I guess it was just the  right time to use it to promote the Au site.