This article at Sydney Morning Herald talks about a young couple who were boy-girl friends, living together because they had practical needs for accommodation.

The female - Sally - was subsequently denied NewStart allowance - because the law treats them as a couple living under marriage-like arrangement.

The Administrative Appeals Tribunal found that ... "the absence of commitment and pooled resources outweighed Sally and Stephen's shared bed and household" and ruled that their's was not "marriage-like" arrangement..

This is a good example of social change driving the law.