The Department of Agriculture has just updated the list of countries we can accept samples from. Quite a few have been removed from the list:
We can no longer accept samples from:

• South and Central America

• Most of Asia (Japan, Macau and Singapore remain as exceptions)

• Some Northern European countries (for example Greenland)

We have updated the website to reflect these changes.
They have not been explicit about why these changes have been made, but they do regularly take into account outbreaks of infectious diseases that we do not have in Australia.
You can see our full list of accepted countries on our How To page Practical Horse Genetics – How To