Nothing.As you know,Australia is a country continent so the states can have straight as they are both country and states.
Actually Australia is a country continent which has no different language people or no different types off divisions in between the people as compared to India India has a lot of different languages + religions and also different traditions and culture thus the states in India have been divided on the basis of the above conditions where as Australia is being divided on the basis of directions as you see like Western province and northern province extra Tasmania is left different in the southern part of Australia thus it has been divided into straight lined states.