As someone with custom-made corsets... all those women are wearing them, or took one off immediately before the photo (except the second to last, which has a different shape). In the last photo I am pretty sure I can see the lines and pressure points from a corset. When you take off a corset the shape can hold for a while, especially if you wear one frequently and/or the shape change is extreme.
Interestingly, this type of hourglass shape is easiest to achieve when slightly overweight or on the high end of normal. If you get down to a lower normal weight or if you have a lot of lean mass (and not much fat) you don't have as much movable tissue.
Kind of a nice thing for us weight-loss girls, because a corset can do things for us that it can't do for skinny girls.
I'm not saying an hourglass shape isn't achievable without a corset, for the record (I had an hourglass shape and when I was lean — large chest and hips/bum, with a relatively small waist and flat tummy)... but these photos are extreme examples which you shouldn't expect to achieve without a corset.