It's hardly the same sort of dynamic. No-one other than really keen fans of Kate really cares much what she wears, unless it's because she's flashing again. Further, I think that she is content with her lot and is keen on keeping things running smoothly on the home front, so she's not going to intentionally go out of her way to do something spectacular to draw attention away from William. However, if she suddenly started changing her image and appearance and getting smart new haircuts regularly and wearing a new style of high fashion, sophisticated clothing, and started making an effort to carve out a role for herself independent of her role as William's wife - particularly if she made a point of doing/wearing something of an attention-seeking nature at the same time as William was doing something he had planned and that was important to him - she would certainly attract the attention of the media and the public. Everyone would be engaged and wondering what would happen next in the royal reality show, which is what happened with Charles and Diana.