Well, my entire knowledge of 'typical' European dress and body shape is only from a few short visits as a tourist, plus what I see on TV and in magazines, etc. But I think it's fair to say that, just looking at people in a mall or somewhere, more Americans do seem to be fatter, and more serious obesity is more common here. Again, it matters how you phrase it, whether you say '(all) Americans' or just 'many Americans.'
To some extent it may indeed be a class issue, partly from lack of education about nutrition and health, but also partly for other reasons. Cheaper foods are often more fattening, and grocery stores in poor neighborhoods don't stock much fresh produce. It costs money to join a gym or sports club or take an exercise class. People who do physical work, as opposed to sitting in an office, get accustomed to eating heartier meals.
But there are certainly plenty of fat middle-class people in the US too, so it seems reasonable to note that general cultural difference. It probably has to do with eating more processed foods, and with driving as the main means of transportation -- I have the impression that here there tend to be more overweight people in small towns than in large cities.
What strikes me as unfair is implying that fat people think they look good, that in essence, they're fat because they want to be. For most people, controlling their weight is a constant struggle, and more so the older they get. Healthier, more natural foods take more time and effort to buy (shopping more often) and to prepare (washing, chopping, stirring, measuring, etc.). Regular exercise also takes more time and effort -- going to the gym or the park, joining a sports team or aerobics class, working out on a machine at home. And if you view it from the perspective of taking pleasure in your body, in the physical rather than the mental, then you have to admit that eating only low-calorie foods isn't very pleasant, and neither is exercising.
Certainly both are possible, but following a healthy routine is much easier for people with certain personalities or temperaments -- for example, those who like the structure of rules and schedules, or who enjoy healthy activities like exercise and cooking for their own sake. If you prefer spontaneity, or find books and music fascinating and tennis and stir-frying rather dull, you're out of luck. Mood is another sort of vicious circle: putting forth the extra effort to improve your life is basically much easier if you're already generally contented and motivated, and much harder if you're not. And apparently genetics, metabolism, has a lot to do with it as well.
It just seems to me that sometimes, the people who tend to be the most critical of fat people are the ones who never really had much trouble staying thin -- just as the people who insist on perfectly ironed shirts may often be those who either don't do the ironing themselves, or who don't particularly dislike it.
As for office attire, of course many people no longer wear suits or dresses here either. Even at a traditional company, the bankers/lawyers/stockbrokers/managers/etc. would, but many other employees might not. And here also, universities tend to be among the most casual places to work, and people who iron everything as a matter of course tend to be in older generations.
re Tiermediziner: Do I detect a whiff of personal bias against the veterinary world? (-; What are Wachsjacken anyway, and why do they stink? The pictures on the web just look like ordinary rain jackets. Oilskins maybe? I've only encountered that word in books; I thought it was some historical article of clothing, before water-repellent fabrics had been invented.