^She's a bit famous, of course, for a little person. I can assure you than magazines sell other women to french people: lots of actresses, even more actresses that princesses. And as princesses are concerned, it is Catherine who is the most talked about. French women are interested by this middle-class girl who married Diana's son. Point de Vue often talks about Mary, Maxima, or Letizia: strong and classy women, who are admired by lots of people.
I would add that Charlotte didn't appear on Elle's cover:
she was just evoked on the cover, nothing more. Vogue is too expensive, and too specialized in fashion for french women. I don't talk about fashionistas, but about french women who have a job, a family, and run all the day after the time. If Charlotte is on a cover, it will be on a "tabloid" (I say tabloid to make an opposition to fashion magazines) where we will see pictures of her at a party: this is not good for her image. She's often presented as a socialite - until her "intellectual" interview in Vogue. But not a lot of people are going to read it... If you want to verify what I say,
go on french forums, and read comments about Charlotte. You would be very surprised, people don't like her at all.