He is married to an Australian, which makes him Australian(ish), so you can't deny him because he is from elsewhere.
What is the world coming to when a balding 30 year old Irish guy with bad teeth wins Idol? It means the show has a little more credability, because he is an amazing singer, and easily amongst the best few the show has ever come across. Jess was also great, but Damien is better. His version of the single is better because it has a more defined vocal melody, which didn't make it so bland.