Very good points. It all come to what are the shipping terms. It should be mentioned and agreed to ahead of time. If the buyer does not accept insurance, you shouldn't be held liable for the loss. I will request that insurance and delivery confirmation is mandatory on anything over $100.00.
I'm a Licensed Broker for a freight company here in the Midwest and deal with this on a regular basis. Shipping (mailing) does not cover insurance and receipt. You have proof that you mailed the package (the postal receipt), so your part as the seller is already done, but if the item does not arrive, it shouldn't be your fault if the buyer did not purchase insurance. However, if the buyer is a good customer it wouldn't hurt to make it up to them. Remember, it takes years to build a good customer relationship, but 1 second to lose them.

On the flip side, as a seller, delivery confirmation is your only guarantee that the package was received, its your only protection.

FYI, in the shipping/freight business, insurance is where we make the most of $, odds are that nothing will happen.