... there's plenty of ways that RDF specifically addresses the problems it seeks to address - data interchange, standards definition, KR, mashups - in a distributed web-wide way. RDBMSs address the problems that were faced by programmers at the coal face in the 60s and 70s - Efficient, Standardized, platform-independent data storage and retrieval. The imperative that created a need for RDBMSs in the 60s is not going away, so I doubt databases will be going away any time soon either. In fact they can be exposed to the world as triples without too much trouble. The problem is that developers need more than just data storage and retrieval. They need intelligent data storage and retrieval.