I admire the consistency, but the ammount of posts I see along the lines of "we won't hire Australians anymore" and the absence of posts like "we'll be adding Australia to the list of countries we don't hire from" doesn't fill me with confidence that this is common.

Even before this change plenty of Chinese nationals would likely be employed wherever they were storing data in Australia and MS didn't care about that. I'm not aware of any MS ban on hiring Chinese either. So they were presumably fine with the threat of Chinese nationals inserting back doors, but it's a problem now because it's Australians.