Let me help you explore the inside of a pricey gown from Vera Wang ($1395 retail).
This photo shows a petersham waistband. This is necessary for many women because the gown is strapless and the wearer has very little difference between waist and hip measurements. Without the inner waistband, a very embarrassing moment could scar the wedding if the bride trips while walking down the aisle…. Revelations…
Note the thread shanks to attach the ribbon. This allows the wearer to move freely without the gown binding. It also permits the garment to be worn by several different body types. Also, the ribbon is connected by a pants (or skirt) style hook and eye system; several hooks allow the band to be adjusted to fit.
I have employed this method in my own gowns with a few exceptions. My gowns are custom fitted, so the band is stitched to the front at the vertical bust seams. Then, I either stitch it to the vertical shoulder blade seams or I add a ribbon loop for the band to slide through on these seams.