I interpreted it to mean that Amazon bought trailers they didn't realize they already owned.

The title is rather poorly worded. There is no need for "its own".

Not yet, but soon. First they need to buy the truck trailers to keep in stock, then they need to buy the larger truck trailers to transport the truck trailers during shipping.

If you have Amazon Prime, you can buy downloadable tractor-trailers.

It's not recommended for customers who lack high-speed, unlimited data plans.

they already sell cars. http://www.huffingtonpost.com/2014/01/06/huge-amazon-box-del...