That's certainly true for typical homeowner's insurance, unless you get a special rider, which is generally way overpriced. I have no idea how it works for commercial insurance. But there's at least one company that gets mentioned here regularly for collector-level coin insurance. I can't call it to mind off the top of my head; can someone else?
Those of you that value you collection only for its resale value can take comfort in insurance. Those who have spent a lifetime gathering coins that meant something for other reasons would rather have those coins than the cash they would raise at auction (let alone what some insurance company would pay). At least twenty of our regular posters here have coins that are simply irreplaceable for one reason or another. If you only value your coins for their cash value, perhaps you are in the wrong hobby.
If your irreplaceable coins are stolen, would you rather have a cash settlement that you could use to acquire new one-of-a-kind coins, or nothing at all? Equating "I've insured this item" with "I only value it for its cash value" is not only wrong-headed, it's kind of insulting IMHO. Would you say the same thing about someone who took out life insurance policies for his children?