I think that the insurance carriers also consider your credit score and criminal history.
My wife and I have used Progressive for 11 years now and pay $540 / 6 months for an '09 Z and an '07 Trailblazer full coverage. We have excellent credit scores, no criminal history, live in a decent enough neighborhood and keep both vehicles locked up in the garage. We also pay the premiums up front and avoid the admin fees.