There so many things to comment on about this article that I almost don't know where to start!

Suffice to say that the fact that the kind of solution proposed is possible (even if kludgy) indicates the flexibility and power of the relational model.

In general, never equate a particular implementation's strengths and weaknesses (MS SQL Server) to the strengths and weaknesses of the model (the Relational Model). For what may be the best information regarding the relational model, see http://www.dbdebunk.com