1) Canonical. You could have made the exact same argument as this article 10 years ago and said that there wasn't room for another RedHat. Canonical arrived and proved that yes, there is room for another profitable Linux vendor. I know I use Ubuntu server and am considering support contracts, so there is definitely a market.
2a) So Redhat doesn't have the resources for development that Microsoft has and therefore will produce an inferior product? Have you seen Windows 8? Vista? Money does not guarantee success.
2b) Even without the same resources, the main Linux kernel has an enormous number of top-talent developers working for free. This is a serious economic advantage over traditional closed source companies.
3) Why on earth is the article comparing RedHat to Amazon? One is a Linux distribution vendor, the other is a global internet shopping mall.
I'm sure others can provide more reasons. Or even counterpoints; feel free to rebut ;)