I think what they meant was they wouldn't accept any liability for any loss. If they lost it or broke it, it's your tough luck. And they are entitled to offer those terms. If you accept them, that's all good.
Unless the shipper and the carrier both agree to limit the liability, the carrier can end up paying for the whole loss, even if there isn't any insurance.
Some kind of liabilities can't easily be limited, whether there's insurance in place or not. Employer's liability, and public liability for example. They're the really scary ones, as a court will generally decide if you're liable or not, and whether you're insured or not won't be a factor in the decision. The amounts are usually quite high too, which is why it's always worth having Public Liability insurance as a courier, obviously.