I guess the sea-faring routes between Asia and Australia were responsible for the settling of Australia. You're probably right; the land bridge may not have existed.
However, I am still baffled about why a culture would voluntarily stop developing sea faring technologies that they used previously.
No doubt the fellows out in the deserts didn't build them ~ really can't figure out why you'd need one at Ayers Rock for example ~ but they also got down to Tasmania, and that was before they'd invented much technology related to making clothing.