Oh yes, the size thing drives me mad! (Although I understand the logic).
Although my stretch-waist jeans are a UK16 and fine, if I want to sit down in a button down shirt without embarrassment, it still has to be a UK24. I read - both here and in magazine articles - about people at my weight now slipping comfortably into a UK16 top and bottom, or even less and, well, it's a challenge to my equanimity, let us say!
Don't get me wrong, I don't begrudge anyone their sizes but I guess I'm going to have to be a UK10 before I'm anything like lissom. This feels strange because when I was younger, 100 years ago, Size Ten was definitely skinny, 12 was healthily slim. I may need to reevaluate. Still, at UK16-24, I don't need to be rushing into that reevaluation!