I read The Dark Knight Strikes Again recently. I remember being confused as to why these so-called "Superchix" continued to appear. Are they supposed to tie in to the larger story of heroes and government? What's the deal?
The Superchix are groupies whose predisposition for supporting metahumans made them instant celebrities when Batman's war against the corporate and government controlled criminality came to light.
They have no powers save the media's response to them. Only one of them ever makes any real sense during most of their appearances, but the media and the media-obsessed public attribute meaning to whatever it is they do say whether it be useful or not. Observe:
Why do they even matter during the course of the story?
Because Lex Luthor had stolen, killed, or blackmailed most superheroes out of the crime-fighting business. He then turned the people against superheroes using psychological manipulations of government-controlled media.
The SuperChix are a story-telling element (focused on the Human events in the story) allowing the reader to maintain a connection with how people are responding to the cataclysmic events of the superhumans in the story.
According to one literary analysis of the book that I've found, they are meant to represent the "triumph" of Batman's forces, freed from their presidential ban against performing, and indicating the superheroes entering a more interactive role with pop culture.
Depending on your point of view, they could be seen either as a triumph of freedom, free speech in the favor of superheroes after governmental oppression, or they're a sign that the victory is relatively hollow. Yes, the society is no longer as oppressed by the government, but the most visible indication is three "scantily-clad publicity hungry superhero groupies" who are now free to be on the public airwaves. That would be like the triumph of free media being Miley Cyrus being able to perform "Wrecking Ball" on TV again.