Of course they really can't be blamed for this. After 13 years of identical education, and after 13 years of social trends, and limited feedback, this is who they are in school. Many of them lead interesting and dynamic lives outside the classroom, but they've learned a long time to keep that space separate from their school persona. As a result, they all sound the same.
I'll confess I have no solution here. My methods, while slightly more flexible, still require some degree of standardization and are certainly not unique enough to allow students the ability to undo past damage. Perhaps by the end of the year, when the senior speeches arrive, they'll finally have learned by experience and be able to stand in front of the class and make a difference.