The Guardian may not have enough money to invest in the Australian market - they lost 37 million pounds last year and may run out of cash within a few years (
source). I also wouldn't call them that serious about the US edition (although I do read it regularly). They don't have the resources to make a serious play for the US market, and while they don't, they'll remain a niche news source for Anglophiles, a bit of live blogging of American sport notwithstanding.