Again, if they can provide proof that the item was shipped, they are not going to be held responsible. Their obligation only lasts until the point that the item leaves their possession. Do you really, truly think that any court is going to hold a seller responsible for the postal service's up?
Do you think any court is going to find a consumer liable for not recieving a product they paid for when they have no control over the packing or shipping process? The fault is with amazon who has a special business account with the postal service and can take steps to identify and troubleshoot how the package was lost.
They assume liability until the item has been delivered to the customer at which point the customer is responsible for the merchandise. Its the businesses responsibility to get it to the customer. If their postal service loses the package they need to refund it or send a replacement and then take the issue up with the post office.
That's standard business law. It's also why amazon will re-send a package if you report it as never having been delivered because they know it will be their responsibility. They will then contact the post office and investigate if they feel its worth it.