Amazon US usually sells the pack for $57ish, so I suspect this is a Black Friday deal.
At $12.50/blade this is cheaper than the previous lowest price on OzBargain ($13.60/blade in a 2 pack).
Put another way, it is a 3 pack for $2.50 less than the Australian 2 pack RRP.
Thanks for posting mate. I saw this about 1am and ordered but fell asleep before getting it up here. Good deal for those with compatible products.
Edit: And it is part of their Black Friday specials.