The author is talking about physical infrastructure as adding value, and they're right, but there's a middle layer that cloud vendors add to their managed tools -- things like auto backup, upgrade and resize for mysql.
These are enhancements to open source DBs etc that cloud vendors keep in-house as secret sauce. This makes the stock version of open source software hard to operate in the way AMZN / GOOG operate it, while still allowing AMZN / GOOG to benefit from community effort without giving much back.