Liability insurances costs?

if you own an altima 97 for instance you would pay like 800 $ a year for liability only, and let's say a mercedes or bmw from the same year and similar in size to the altima, why would you pay more for liability insurance? after all liability only covers the damage that you would case in an accident, in that respect all cars which are similar are capable of causing similar damages. I will accept to pay more if the insurance would also cover damage to my own car, in that case i would understand it cost more to repair an expensive car. isn't that a rip off, just like when the ins companies charge by zipcode, it should be based on driving records, age, experience, etc.