I've missed a lot of this thread since it originally appeared but I am not surprised by your comment Moonraker! For a start you're Aussie so you have had a different perspective on outdoor Australia anyway, and I could never understand the "indoors" lifestyle in summer when I came on trips here to visit family and friends before we moved.
Just about every friend I have here who's had a baby has been told they are vitamin D deficient, in fact there's been stuff in the news about it not so long ago. And not just pregnant women. You don't actually have to get a lot of daylight to have enough vitamin D. I do think amongst Australians there's definitely more of a culture of staying indoors when it's hot. And having aircon on a lot. Or maybe our Aussie family and friends here are unusual, but I don't get that impression. I do find keeping the house dark and curtains drawn also to be soul destroying but again those who've grown up with it, know that it's a sensible way to keep the house cool and you pay for it if you don't.