Yup, it's a big old simplification - reality is pretty messy.

As to your specific examples, Kucinich was, indeed, quite an outlier and is no longer in congress. Bachmann's views are probably quite a bit closer to that of the median voter. Even just yesterday she was making wishy-washy statements on the debt limit fight and over at redstate.com you can read Erick Erickson denouncing Republican leaders for "caving on everything".