Yikes, thats a $20,000usd difference! Maybe partially something to do with import costs/tariffs/taxes on the JD? Can't imagine its worth that much more myself, but i don't have any experience with those models.
All tractors are imported into Australia, and from what I know, barring any free-trade agreements (which we have with the US, Korea and Japan), tractors from each country would be subject to the same import and tax treatment.