I'm saying this in ignorance, since I haven't delved enough into either GaGa or Ke$ha, and this is conceptual as much as (or more than) it is aural, but GaGa is everyone is a star, it all can be art, which can come from the Merry Pranksters and the Dead and the Airplane as much as from Warhol and Madonna, but it's definitely an artist's viewpoint, someone who's committed to long-term creation, building your art over many nights and many dances, not the moment's pie-in-your-face explosion. And Ke$ha may actually be a long-term artist (though my money's not on it), but her sound and persona are the blotto and the instant blat.