Not sure how other companies work, but I work at Progressive and we don't actually underwrite the home insurance or renter's policies. They use two companies, Homesite and another that I can't recall. But we are essentially a middleman, and the only benefit is you get a discount for having more than one policy "through" Progressive. They seem to be moving toward wanting to actually underwrite home policies, but that might not happen for a while.
Not sure how our rates compare since I work mostly with auto policies, but it's worth checking out if you already have auto insurance through them.