Actually XML is more "reach" format than JSON. XML nodes have attributes and values, when in JSON - values only. And lot of databases are "document-oriented": http://en.wikipedia.org/wiki/Document-oriented_database and what is matters in comparison is parsing performance and size. JSON just more compact, but not better in all aspects. I think XML is an excellent format, especially when size matters less than "dimensions" of presented information. I think it's perfect format for RSS and for REST API and for web-pages.