[Crunchified]

It is NOT the insurance company's job to replace a worn-out roof. That is YOUR responsibility! If a roof on your home is not up to the proven (albeit occasional) stresses of your local environment (including snowfall, winds, volcanic ash, etc.), whether due to quality, design, or wear, I see no reason why the insurer should not modify its indemnity. I will grant you that a decent insurer would allow you to petition for a review based on any verifiable additional information that you, as owner and insured, might be able to present.