Hi DC -
You definitely get your point across well in your article. The only things I would add are:
1) You don't need to store native XML in the database in order to take advantage of SQL Server's XML functionality (that seems to be one of your larger concerns); you might have noticed that the XML I used in these articles was not stored in a table on the server
2) XQuery provides a simple means of querying your XML data based on just about any criteria you care to use (whether you want to retrieve albums by Artist, Genre, Producer, Label, etc.)
3) XML is not designed to be a replacement for the SQL model
SQL and XML have different goals, different priorities, and I personally believe it's a case of selecting the right tool for the job. After all is said and done, like SQL, XML is just another tool in the toolbox.