Aussie1 you are only partially correct. I also hold an Australian license.
If you meet the aeronautical experience requirements then you do NOT have to hold any US certificates to apply for a US ATP.
Here is a link and an excerpt from the current regulations.
ATP Requirements 61.151
Check out this link for current regulations.
This is a frequent topic
"§61.153 Eligibility requirements: General.
To be eligible for an airline transport pilot certificate, a person must:
(a) Be at least 23 years of age;
(b) Be able to read, speak, write, and understand the English language. If the applicant is unable to meet one of these requirements due to medical reasons, then the Administrator may place such operating limitations on that applicant's pilot certificate as are necessary for the safe operation of the aircraft;
(c) Be of good moral character;
(d) Meet at least one of the following requirements:
(1) Hold at least a commercial pilot certificate and an instrument rating;
(2) Meet the military experience requirements under §61.73 of this part to qualify for a commercial pilot certificate, and an instrument rating if the person is a rated military pilot or former rated military pilot of an Armed Force of the United States; or
(3) Hold either a foreign airline transport pilot or foreign commercial pilot license and an instrument rating, without limitations, issued by a contracting State to the Convention on International Civil Aviation.
(e) Meet the aeronautical experience requirements of this subpart that apply to the aircraft category and class rating sought before applying for the practical test;
(f) Pass a knowledge test on the aeronautical knowledge areas of §61.155(c) of this part that apply to the aircraft category and class rating sought;
(g) Pass the practical test on the areas of operation listed in §61.157(e) of this part that apply to the aircraft category and class rating sought; and
(h) Comply with the sections of this part that apply to the aircraft category and class rating sought.
[Doc. No. 25910, 62 FR 16298, Apr. 4, 1997; Amdt. 61-103, 62 FR 40905, July 30, 1997]