This is such an interesting topic.
If I open a fresh-fruit stand and refuse to sell the Chromecast and I being anti-competitive? How about if I grow my own fresh-fruit and refuse to sell yours in my stand?
The whole reason for me to spend money running my own store it to sell my stuff, not yours.
What about if Apple open an "Apple Store" and refuse to sell Microsoft products? Ford dealership refusing to sell GM?
It's Amazon's store, they can sell whatever they want, or not sell whatever they want. If you don't like it, shop elsewhere.