I agree that when it's your job to sell something you will look the best you can too. I wouldn't go to a hairdresser with a really bad haircut (though again bad is subjective), or to a beautician that had a terrible nails.
They'll have worked damn hard at their bodies, I know an actress/model and it's very hard work and I wouldn't like to be on such restrictive diets and strict regimes she is. But that's her job and her choice.
Perfect hair and make-up on a model on an advert...they'll be a whole team behind that. Not saying their complexion may not be flawless and hair perfect but after seeing artists at work, they could easily have very not-flawless and hair that normally goes all over the place.
After seeing a fair few of overweight people become 'fitness freaks' and going really at it, I can honestly say that while not all will look like those models because it's also due to body shape, they could easily get the muscles- either through very hard work or, like my friend, obsessive gyming and dieting. It's just most people don't have the need and motivation because their livelihoods don't depend on it, they're doing it to feel good, lose some weight, be healthy or just for the horny rush. I could have a six-pack if I had the drive my friend does, I don't and I don't want to.