I guess the RDF model is a little simpler. It's all just triples, that can be automatically combined with other triples, and thereby inferences can be drawn. Does this actually produce anything useful, though? I don't see the killer app. Theoretically a lot of people are talking about combining RDF and ontologies from mulktiple sources too find knowledge that isn't obvious from any one source. However, no one's actually publishing their RDF. They're all transforming to HTML and publishing that.
That's part of it. The other part is that this is a lot like the problem with OO and the holy grail for a generic "Customer object". The problem is that your definition of a customer is likely to be different than my definition of a customer. In the same vein, the RDF triples defined by one group of developers is unlikely to match those defined by another one. The basic problem is vocabulary - go read this book on the creation of the OED to see how hard a problem that is :)