Vince Lia couldn't play for NZ because he'd already played for Australia in an Official Competition, and wasn't eligible for NZ at the time.
Andrew Durante never played for Australia.
Marco was eligible to play for Chile until he played for us in an official competition.
Until Fitzgerald plays for NZ in an official competition match, he can switch allegiances.
You have to have held the other nationality at the time you played for the other country for a friendly to be able to change. Because Durante never played for Australia in that friendly, he thus was deemed never to have played international football (for anyone) so when he played his 1st international friendly, he had dual nationality and was not tied to Australia. If subsequent to Durante playing for us (for example) in a friendly only, he would still have been able to switch to Australia. Fitzgerald didn't have the option of choosing another nation like Marco thus, to make the switch to another nationality (Japan) he can't have ever had taken the field for NZ because at the time of that game for NZ, he was not eligible for Japan regardless if it was an official game or not. To be able to change nationalities, you much have had another one at the time you played in any international game (although competition games tie you to that country)
Article 17 Acquisition of a new nationality
Any Player who ... [assumes] a new nationality and who has not played international football [in a match ... in an official competition of any category or any type of football for one Association] shall be eligible to play for the new representative team only if he fulfills one of the following conditions:
(a) He was born on the territory of the relevant Association;
(b) His biological mother or biological father was born on the territory of the relevant Association;
(c) His grandmother or grandfather was born on the territory of the relevant Association;
(d) He has lived continuously for at least five years after reaching the age of 18 on the territory of the relevant Association.
He has played for NZ so the rest is irrelevant.
Actually Fitzgerald has not played in a full International for NZ, so that is not a reason he could not change allegiance, as Wibble has said, if a player has not played in an official competition for a country then they are free to change allegiance.
As per Big Pete's posting http://www.yellowfever.co.nz/categories/kiwi-players-overseas/topics/the-all-new-michael-fitzgerald-thread-albirex-niigata?page=9#post_926434 Rufer stated something about the club being concerned that Fitzgerald wouldn't get his visa, which is incorrect as Fitzgerald must've had a visa otherwise he couldn't have stayed in Japan. I think Rufer meant his citizenship, which means Fitzgerald was in the process of applying for citizenship when he played for NZ.
As per Article 17 or 7 quoted by Vader and Wibble - I think you'll find Fitzgerald actually meets condition (d). He has lived in Japan since he was 16. He attended a Soccer High School and finished his High School years in Japan. He was signed by Niigata when he finished High School http://www.seiritsu-int.com/contents/2007/09/, therefore he has lived in Japan continuously for 8 years and condition (d) only requires 5 years.
The whole of the argument is irrelevant. Fitzgerald is only one of 72 Centrebacks in the J League eligible to play for Japan, so highly unlikely that he would ever get called up to play for Japan. The chances of him being selected above a Japanese born player is not likely to occur.
The other point as mentioned previously is regardless of what FIFA statutes state, Japan is a country that does not allow dual citizenship ie: you can't represent another country and retain Japanese citizenship. So while Fitzgerald lives and plays in Japan as a citizen, he will not play for another country.
FIFA does not rule the world. Countries have their own laws, and country laws around immigration aren't written to suit FIFA.
My point is - Japan would revoke Fitzgeralds' citizenship, if he chose to play for another country. They would see it as disloyal, after he applied for and then accepted Japanese citizenship. You're talking about a country who even though there's International laws against hunting whales, they totally disregard them and prosecute foreigners who get in their way, trying to stop them.
When Fitzgerald accepted Japanese citizenship he would have been made aware of the fact he was pledging allegiance to Japan only and therefore revoked allegiance to any other nation. While he remains a Japanese National he will never play for any other country, unless he's prepared to give up his Japanese citizenship.
If he's secured a 3 year contract as a Japanese Citizen (posted on his personal thread), it is highly unlikely he would give up his Japanese Citizenship to play for any other country.