Australians don't sing songs in Australian accents unless it's a novelty song or a bush ballad (though there are exceptions such as Redgum's anti Vietnam war song, I Was Only 19). How far do you think Urban would have got if he had sung the way he talks?
(I always enjoy hearing English singers like Peter Gabriel, Phil Collins and Kate Bush sing words like 'can't' and 'last' the English way. When Robert Plant sings 'the truth will come to you at last' the English way in Stairway To Heaven it's the way it should be).
Australian dates Australian -well well! It's a small country in terms of population and 'celebrities' are thin on the ground.