This is true. However, the point of the article is to promote the creation of a simple and consistent XML-RPC or similar interface for use in querying databases.
If every database server recognized a simple, albeit limited, RPC call, this would eliminate the need to struggle with database middleware, vendor specific libraries, etc in many situations.
While it's true that many of the individual pieces needed to do this are out there, and have been for some time, there isn't the database equivalent of RSS that provides a reasonably vendor neutral interface. Based on my recent experience, such a thing is badly needed, as I spent probably 80% of my time trying to figure out how to get a DB specific library to work correctly in different installation scenarios versus debugging the application itself.
Stated simply, SQL provides a reasonably vendor neutral way to express queries. What's needed now is an Internet friendly way to deliver queries to DB servers, without getting bogged down in unnecessarily bloated middleware, external libraries, etc.