I would guess they are really +/- 50% for Progressive because credit really does play a large part. I can't imagine they won't get sued again by these companies for falsely posting their rates as higher, so that they can sell more policies with the companies that actually pay them.
I love how he says in his letter "even assuming that your letter is sufficiently original to be copyrightable, and that you register the copyright, the posting of your letter will be fair use and hence not actionable"