Amazon.com has a focus on retail. They sell stuff and the Kindle (including Kindle Fire) line is just a medium to get it to the customer. If FedEx and others kicked the bucket tomorrow and Amazon felt UPS was too strong as a vendor, they'd probably start their own logistics department. If they felt Comcast was too dominant, they'd probably want to do something about that as well.
Google's focus is arguably its services (which it uses to push ads). Apple is stubbornly a devices (hardware) company.
However, it is unclear what Microsoft's angle is here. Do they want to make money selling software through OEMs? It doesn't seem like they want to push prices of hardware down. They make too much money off of enterprise software to cut that arm off. Online services does not make enough money to let it completely cannibalize the software licensing cash cow yet.
I am glad I don't run Microsoft. I would be lost.