As Americans we're often overly practical. To that end the big t-shirt has become the "cover-up" for most beach excursions. I was very happy to see the young ladies around Sydney sporting more thoughtfully designed cover-ups. My guess is it's a cultural thing - that they don't "go to the beach" like we do. I think in Sydney it is more like how we "go to the gym" on a Saturday or after work - just another thing to do during a busy day in paradise.
PS. A few of you commented that the light in Australia seems very different. You're right. Actually, it is not that different - but since they are going into Winter the sun is much lower in the sky as opposed to in the Summer when it is very high and has a harsh shadowing effect. That's why I could take a midday beach shot without all of the hard light reflecting off of the sand. Anyway, I don't know if you needed to know that, but if I am in Sydney or Melbourne every April for the next few years you will know why.