I agree with a lot of the responses above. It's funny, if you've been reading/hearing about how they're using body mass index as a measuring tool at schools and it's freaking kids out because a lot of them are out of the "acceptable" range, and are upset about it, it reminds you of this question of clothing sizes. BMI is a really vague tool because it doesn't take into account what you're actually composed of, so a well-muscled marine could sit down and plug in his stats and the BMI charts would tell him he is overweight. Except that he's 5'8" and 170 pounds of solid muscle. If he then went to a sports clinic that has hydrostatic weighing and floated in the tank, he would probably get completely different results that tell him he has 9% body fat and is in superb physical shape. How confusing.
No matter what the clothing industry says, I don't think there are any standards for clothing sizes that regulate things as tightly as footwear sizes, but I could be wrong about that. And there's so much pressure in our culture about how we look, and it threatens to define who we are if we don't fight it. It seems like I hear all the time from friends and even coworkers this tone of guilt about what they're eating or not eating. Like, I'm sitting at my desk at lunchtime eating a sandwich, and one walks by and says, 'what's that you're eating?' and I say "turkey meatloaf sandwich', and she says, 'God you're so good, always eating healthy, I've got to start eating healthy' And there are similar conversations about working out. And these conversations always leave me feeling vaguely defensive and guilty and I don't know why.
I spent like 15 years of my life stuggling with food and weight stuff and it took at long time to recover from that. I still have to remind myself just about daily that I'm ok just the way I am, especially after someone I've just met makes a resentful comment about how 'healthy' or 'little' I am. I try to tell myself that the size and shape of my body, my eye color, hair color, foot size, and even voice are all governed to a large extent by my DNA, by the splicing of chromosomes that both my parents gave when they conceived the egg that is me. So I'll never have a butt like Jessica Alba even if I work out all day long. And I'll probably never build big muscles because I've observed that neither of my parents do. And I think the body size I am is in my genes too. And that comforts me.
What I really hate is that our culture still defines women's value in their clothing size. Female gymnasts still get their weight listed in the first two sentences of introductory interview description about them. I notice male gymnasts don't. How irritating. And magazines are either cluck-clucking about a star's change in clothing size or publishing articles about how to drop a clothing size. It's really hard not to see it or hear it--I had to stop subscribing to women's magazines for a long time. But I guess it's everywhere so it's hard to avoid completely. But it makes no more sense to expect all women to be within a short range of sizes than it does to walk in the woods and expect that all the songbirds are going to be the same size.
Sorry that was so long.