Not any more, USPS was only used for shipping anyway.
Amazon has shifted to vertical integration wherever they can - they run everything they can, from air freight (with https://en.wikipedia.org/wiki/Amazon_Air) over their infamous warehouses to last-mile delivery with either in-house staff or "contractor" schemes set up to avoid labor regulations.
It has little to do with technological innovation.
These two statements contradict each other. The thing that Amazon does extremely well is logistics and that is core to their marketplace, not something else to the side.
Amazon.com in my opinion is a logistics company who happens to have a Website that sells products.
Amazon moves an item from point a to point b, and they do it fast and efficient enough that people go back to them again and again.
Last month, I ordered two pairs of jeans and a t-shirt from Eddie Bauer. They arrived in three different packages after about 10 days. With Amazon, it would have been 1 package that arrives the next morning or the following day.
If Amazon is abusing its position, substantial fines or regulations are the right solution in my opinion. I’m absolutely not in favor of nationalization. Any kind of government run facility, in my experience, is mind mumbling horrible at their job. They have no incentive to compete - which might eliminate bad behavior but it also makes for a terrible customer experience. Nationalizing Amazon is no different than just killing the company entirely.
Nonetheless as a semi-monopoly you are rarely compelled to innovate like a smaller company is.
I heard similar excuses back in the IE6 heyday for how improving the browser was "hard". Realistically 94% market share just meant that it wasn't broken from Microsoft's perspective.
Amazon does not do business in US only