I think the better analogy is the post office.
You pay shipping to receive packages (to the post office). You also pay for the content of those packages (to whoever you bought the item(s) from).
Now more and more people start ordering stuff from Amazon. The local post office realizes that their mail trucks are filling up and they're unable to pick up all the packages they need. Some of the packages get left behind, some get crammed into the truck (and end up damaged), some make it through.
They also notice that a third of all packages have Amazon logos.
Does the post office:
A) Use the extra money it has been receiving from postage fees to upgrade it's fleet, buy more trucks, hire more drivers, etc.
B) Pick up on Amazon's generous offer to have some items already stocked, packaged, and automatically labeled next to the Post office so that commonly ordered items can be transferred locally instead of going through the USPS's now heavily taxed fleet?
C) Extort money from Amazon in exchange for their customers receiving their packages in a timely and undamaged fashion (which their customers are already paying for).
Now you can say the main difference is that the post office is charging per package vs selling a service to its customers where they can receive a certain amount of mail (say in pounds) per day. Either way though a service is being promised, paid for, but not fully delivered.
And now to add self interest:
What if you got an ad flyer from your local post office with "Now you can order movies and books from the USPS!" while at the same time movies and books that you are paying shipping to receive from Amazon are getting delayed, crushed, or lost.