This article shows relative "cloud" revenues numbers between Amazon, IBM, Microsoft, and Google. In this context, Amazon doesn't look that big.
http://finance.yahoo.com/news/official-amazon-strongest-clou...
http://finance.yahoo.com/news/official-amazon-strongest-clou...
As for Microsoft, quoting directly from your link: "One person has told Business Insider that Azure revenue is at $1 billion lifetime since its debut in 2011, but is accelerating quickly."