The argument makes a lot of sense, but why is Amazon in this list? It is true that Amazon is in the war for control. But that war is for control of the data center, not for control of the web.
Kindle, I suspect.
Remember, this is being written by Tim O'Reilly, a person who has reason to know and care about the Kindle's position in the digital-text marketplace and the relative openness (or lack of openness) of the platform.
I agree that Amazon Web Services doesn't seem to belong on this list. AWS is a powerful offering, but it's not as if Amazon has an exclusive lock on the Linux virtual server business. I believe that even their provisioning API is in the process of being cloned in open source.
Kindle does have a potential to become a walled-garden ecosystem reminiscent to Apple. There's nothing Kindle wants more than to become an iPod of books and will very likely curb the Web experience on Kindle to suit its business needs.
Edit: My comment reads like I'm getting defensive for Amazon, and or bashing Apple. I'm not.
Amazon, Apple, and Google are three heavyweights with a slightly different focus and strengths, but who find themselves competing more and more often for a sort of internet consumer dominance.
They compete at several platforms: 1. The storefront (iTunes and Amazon, Google's in there as search and recommendations). 2. The datacenter / cloud (AWS, MobileMe, Docs / Gmail / more to come from Google) 3. Mobile devices (iPhone + iPod, Android, Kindle)
There are other companies competing in each of these areas of course, but these three companies really excel at taking over markets (very smart people running them) and it's going to be interesting to see them going head to head as they reach into each others core markets.
Plus I think they'll destroy most other competitors in each of these areas as they battle it out.
For some reason, even though I'm aware of all (or at least most) of the arguments that place value in Facebook / Twitter etc. I still wouldn't feel comfortable investing in it. I'm probably dating myself pretty badly, but they look fluffy to me.