Wolf analyzes these series and acknowledges the changing focus of "girl" books.
Since women have been writing for and about girls, the core of the tradition has been the opposition between the rebel and the popular, often wealthy antiheroine. Sara Crewe in Frances Hodgson Burnett's "Little Princess" loses her social standing and is tormented by the school's alpha girls, but by the end of the story we see them brought low. In "Little Women," Jo March's criticism of "ladylike" social norms is challenged by an invitation to a ball; while Meg, the eldest girl, is taken in by the wealthy daughters of the house and given a makeover — which is meant to reveal not her victory as a character but her weakness.
This tradition carried on powerfully through the 20th century. Even modern remakes, like "Clueless," show the popular, superficial girl undergoing a humbling and an awakening, as she begins to question her allegiance to conformity and status.
My very few cents worth on the subject are:
1) I have not read them. I have a copy of the A-List that I picked up at TLA a few years ago. I will have to add it to the stack. My entlings have always preferred books about girls who "kick butt" (quote from Tamora Pierce) with wands or swords or are martial arts experts.
2) Parents may be "shocked, shocked" at the content and themes of these books but I would bet good money that while daughter dearest is reading Gossip Girls and the A-List upstairs, Mom and Dad are watching Desperate Housewives or Footballers Wives (if they are BBC Americans) downstairs. Maybe they are all watching it together as a family. When shows like The O.C. and their ilk get the ratings, it is not a surprise that it spills over into our teens reading material. Publishers are just trying to compete.