I'd say Dita's lovely waist comes from having certain body proportions - wearing a corset for extended periods of time can lead to lazy abdominal muscles, so it can actually be counterproductive to the creation of a corsetless slender waist. It's a nice - almost erotic - story to say corsets caused it, but the truth is probably targeted exercise to enhance the torso nature gave her in the first place.
I have a tiny waist purely from the bone structure of what's above and below it; that swooping inwards curve on the side maintains itself, no need for any assistance. On the other hand, it's far from ideal; I wish I were shaped more like a model, so I could wear today's fashion, instead of looking like a relic from the 1950's. Anything that fits on the legs gapes at the waist, and after trying on the 120th pair of trousers, you realise your body type is a total misfit even when in top shape, and you don't have Dita's wardrobe resources.