Plus Delta's Australian too.
There are many amazing Australian artists.
The Veronicas also follow your rules. And there's a nice up-and-coming artist called
Stephanie McIntosh. Both of these two acts perform easy to digest mainstream rock music.
Besides that, I strongly recommend
Lily Allen. Other than foul language, she is simply AMAZING. Her music will be going to the US early next year since it's already a big UK hit and her single was also an Australian hit. She's a summer tunes girl with clever use of samples. A genius really.