FLF, I think you are right to an extent, it does make a difference. I have very little body fat and a BMI of around 20, but have 37" hips which I don't think would ever go much smaller than that because that's the size of my pelvis!
However clothes sizes have changed such a huge amount, even in the past few years. In the late 90s, I weighed around 8 stone (am 5'8") and I was a size 10-12. I would never, ever have fitted in size 10 Topshop jeans, but I do now, even though I am just over a stone heavier than I was then.
I do find it worrying. I have lost quite a lot of weight in the past few years, and have been told recently that I've "gone too far" and look gaunt and even ill! Cheers guys! Before I lost the weight, I was overweight - I am now towards the lower end of normal. I would say far from size 0 changing our perceptions of what's normal, the fact that there are now so many obese people has changed our view of what is normal. Years ago you simply didn't see so many people, especially young people, who were size 18/20+ and so people who were on the low end of average weight were not considered to be stick insects.
It is very hard with all these conflicting messages, as I know because I've been on both sides of the fence, so to speak. But I do find it worrying that being overweight is being normalised. It is dangerous and unhealthy.