The difference is that Louise would automatically have become a Princess whilst the children of Princesses automatically assume the status of their father so Princesses Anne and Margaret's children would never have been Royal anyway. It has never been tradition to interfere with this precedence. Even George V's only daughter Princess Mary didn't have Royal children. They took the status of their father who was an Earl. This is why I never understand why Princess Anne is held up as an example for not giving her children Royal titles as it was never an option in the first place.