I was curious to see what kind of difference this would make, so I did some shopping around. Pricing for the complete series of The Thick of It was $90 at its cheapest (surprisingly, at the ABC store) and $95 at Sanity. Series 7 of George Gently $35 was the best price I could find, for a total of $125 for both.
amazon.co.uk sold them to me, along with a book I was wanting, for $105. Even if GST had been applicable, at 10%, the transaction would have cost $115.50, still saving $10.
Just for comparison's sake I did a search on Dr Who, the 12th doctor DVD set. Sanity wants $79.99 for it; amazon.co.uk is asking 19 pounds sterling. Double that and add $10 for postage, plus 10% GST, I'm still way ahead. I really don't think the GST addition is going to help Aussie retailers, but it will add to the government coffers.