Statistics wise, Shark attacks are very uncommon, and considering how many people go and swim without getting attacked, we're pretty safe. Bare in mind that the attack on the weekend is the only known attack at a beach where Shark countermeasures (shark lines) were in place. The jellyfish problem is mainly in northern Queensland, and is seasonal, so in Jellyfish season, some beaches are literally closed down. I understand others employ nets, and if you are going in anyway you could wear a skin suit, so any tentacles don't reach your skin. I live in Victoria though, and we have no such problem, just the occasional man-o-war jellyfish that hurts like hell but will not kill you. I swim a lot in summer at the beach.
Seriously, if you've grown up here it's just the way things are, poisoness snakes and heat are just a reality in the Summer that you get used to. Like most places, if you lived there you'd get to know the local dangers and how to avoid them.
It is a great source of national pride though, and an Australian will always feel good when some outlander jumps a mile high on seeing a snake.
I have seen Dingos on Fraser Island, which has a large population.