32DD isn't a particularly large size, the average is 36D, and the high back size is because a lot of places don't size very well and offer a too big back size and a too small cup size, or bras which are designed to create cleavage but not actually fit properly. The shape of breasts can differ quite a bit as well, someone may have the same volume but not have the cleavage compared to another.
I mean for instance a 30FF and a 34D are of roughly the same overbust measurement, that's not to say they would look identical, but there is no such thing as "size DD, F, A etc breasts", a different backsize makes them very different things.