As I work in advertising and also am a graphic artist, I know first hand how much images are manipulated.

HERE IS A GREAT EXAMPLE of how a photo is completely retouched before going to print. Gives you an idea of how different the actual bodies and faces of models are different than the photos we see in print.
Mouse-over the image and you see the original photo before being retouched.

Face - original photo and retouched for print
http://homepage.mac.com/gapodaca/digital/bikini/bikini1.html

Body - original photo and retouched for print
http://homepage.mac.com/gapodaca/digital/bikini/bikini2.html

Look at how even her arm is made thinner as well as her waist and hips, while her breasts are made to look larger. And, of course, the entire
surface of her skin is smoothed out of pores to look like a plastic surface.