I have no interest in 'defending' Kate/Katie, but its not like she went out there is a cropped top, and low-slung jeans. The picture was taken from lower than waist-height, and she was wearing a jacket that, has she been photographed from the front and at normal height, would not have revealed her stretch marks. I think it is beyond even the likes of Tom and Katie, to stage stretch marks.
I agree with you on the maternity bra front, but I really think you are looking too deeply into these stretch marks