Darkeyes it's perfectly possible for someone who's hovering around the 5' mark to be overweight (not necessarily fat) at a size 12. Which, as Talkinpeace says, has crept up, measurement-wise, over the years anyway.
People being overweight (again, not fat per se) has become so normalised that a slim body, especially a slim body in the lower part of the healthy BMI range - say 18.5-22 - has almost become some sort of unattainable 'ideal'.
As I said upthread, most people, when you look around you, are even a little bit overweight, simply because it's just so much easier to be this way. It takes concerted effort it to be.
ICBINEG, no most people don't eat when full. Most people do however, eat when they're not hungry. Or even at just the very first pang of hunger.
I find it weird/annoying that wanting to be slim - to have the sort of body that nature intended before our sedentary, mass availability of food lifestyles got in the way - is something to be sneered at. That making an effort not to put on weight is a questionable thing - something that will surely lead you down the road of an eating disorder.
For me, this way of eating is something I can easily work into my lifestyle, without feeling like I'm depriving myself daily, and it allows me to enjoy food most of the time. I love salad. I like vegetables. I also adore cheese. I like wine. I like cake. I love flavours. I love food. Eating 'healthily and cutting out the junk' is all very noble, but it's not much fun when it's every day for the rest of your life. This way of eating doesn't impact on another soul, since no-one but my DH knows about - I don't talk about it (except online when invited to by an OP) because nobody is interested!
If it's not for you, that's fine. But given that it gives me the best of both worlds - eating what I want and being slim - I'm going to carry on.