Missing isn't broken: data validation and freedom on the Semantic Web by Dan Brickley. A good outline of one part of the webiness of RDF - missing parts do not break things. This seems to be one of the sticking points for people familiar with XML apart from taking RDF's XML syntax to be equivalent to RDF's model.
I've spoken on the webiness of RDF compared to XML before in my presentation at XML Europe 2002 in slide 17: webiness but I think my argument needs a polish.