Interesting you should ask that.
First of all Temuera Morrison, who plays the clones in the prequels, is not Australian. He is New Zealand born and plays them with a New Zealander accent.
On the other hand, Dee Bradley Baker, who plays the clones in the clone wars, is American but plays the clones with a fake impression of a somewhat incorrect Australian accent. This is probably what confuses many people but it never bothered me too much since I love the clone wars and the clones in it!
Although I probably would’ve liked a little more consistency between the two. I also don’t really like the idea of an American impersonating Aussies so bizarrely.