article for XML.Com on extending RSS that covers the selling points of an RDF approach.
Ayers makes RDF formats, which are called vocabularies, sound like an object-oriented inheritance hierarchy:
A common scenario is that a general purpose vocabulary contains a term close to what we're looking for, but our requirement is more specific. The solution here is to define our own term as a subclass or subproperty of the existing term (depending whether the term applies to an entity or a relationship between entities). Thus the child class (or property) takes on the same characteristics as its parent, in addition to anything specific to the child.