IANAL, but Australia and the US have a free trade agreement that specifically includes patent rights and one of the strongest arguments against its ratification here was that Australian developers would be subject to frivolous patent troll lawsuits just as they are there.
If that is the case (a big if), I suppose there could be some legal implication in the US, but you'd have to ask a patent lawyer with intimate knowledge of the FT agreement to be sure.
In the IP sphere, free trade agreements are more often focused on the types of laws countries must put in place to protect (or limit, depending on your point of view :)) IP within their own country. So, for example, the US-Australian FTA requires that both countries provides for copyright to exist for at least the author's life + 70 years, or that the only grounds for the revocation of a patent are those that would mean the initial filing was invalid.
The USFTA doesn't automatically mean that Australian IP decisions gain legal significance in the US, or vice versa. For this decision to actually have any impact on Amazon's patent in the US, someone would have to litigate it. The Australian decision could certainly be used as evidence in that litigation (as the questions of novelty would be similar), but as noted about would not have any binding authority.
Thanks for the clarification. A bit off-topic but are you sure about the author's life + 70 years copyright agreement? I remember during the controversy where copies of Orwell's "1984" was remotely wiped off a number of Kindle's, there was some discussion about how Orwell's works were now out of copyright in Australia (and elsewhere) but are not in the US. (eg. http://ebooks.adelaide.edu.au/o/orwell/george/)
If that is the case (a big if), I suppose there could be some legal implication in the US, but you'd have to ask a patent lawyer with intimate knowledge of the FT agreement to be sure.