Its entirely up to you whether to take out travel insurance or not.
I am not certain how true it is that you would be covered by medicare for treatment within Australia.
I do know that from first setting foot on Australian soil our 457 visa people (from Pakistan, Philippines etc though) have to have private medical cover. Only the correct website etc can provide you with accurate details on that.
Travel insurance would cover you for such things as flying you back home on your becoming quadriplegic following a motor accident etc.
Its a bit like household insurance - you can take your chance or you can take the insurance- its up to you to assess the cover and the risk.