Turns out, musicplasma uses a product called ThinkMap, which based on J2EE. ThinkMap's whitepapers make no mention of whether they are using Topic Maps, RDF, OWL or some proprietary technology under the covers. They do have an XML configuration file that makes it very easy to use, combined with CSS styling for the presentation.
Very cool product. It would be nice to see some of the same visual presentation features in TMNav, or Ontopia's Omnigator.
Correction: Just got a comment from the musicplasma guys that they are NOT using ThinkMap engine, but have rolled their own. It was the Sony Music License engine, that used ThinkMap. Still, all of these visual representations certainly resemble Topic Maps. It would be nice if they could all adopt the Topic Map standard for interoperability, instead of going the proprietary route.
Update: Just heard from the ThinkMap folks, and they said, "Thinkmap does not use topic maps, but rather uses tables from a relational database (or practically any other data source, for that matter)." Ditto my comment above. Hopefully some of these companies will adopt some of the Semantic Web standards, to enable interoperability.
See also: TopicMaps