Airbrushing, especially, plays such a big factor. I used to model when I was younger and it's amazing what they can do to a photograph to fit an ideal that is almost genetically impossible.
I did a budoir shoot for my husband's wedding gift a couple years ago and the photographer would do what is called "light airbrushing" - smooth out some "trouble areas" and shading over the stretch marks enough to make you look your best, but still look like you. Even already being aware of the tricks of the trade in the fashion industry, I was floored how natural (and good!) it looked.
My husband hardly noticed until he realized some freckles I have in certain places were missing.
I always have to laugh when some high fashion magazine thinks they've pulled the wool over people's eyes when they do a sloppy job and it's publicly pointed out that they put an actress or model's head on someone else's body and it's so obvious from the picture because the head is 5 or even 10x bigger than the body.