I have been in Adelaide for the past fortnight. (Back in the UK now) It wasn't hot but by no means cold.
Slightly chilly, sure. The other thing I noticed was that when people said, oh no it's going to rain tomorrow; it would rain for an hour and then the sun would come out and it was beautiful.
I've got to be honest, it was good for me to be there in winter after only ever being there in the summer in the past. It wasn't half as bad as I imagined though, I found it was not cold like it is in Northern Europe in the winter and you can still go out and do things. Just take your rain coat.
I even went for a swim at Glenelg which everyone thought was crazy, but I didn't think it was that cold at all.
It was good to see how cold it does get, however if that's the coldest it gets in Adelaide, then I'm in. I could absolutely live with that.