There are several reasons why you've never heard of Topic Maps.
First of all, topic maps are transparent. When you're using a topic map, you don't know it. You find what you're looking for, and you don't care why it was so easy.
The second reason is that nobody owns the techniques of topic mapping, or the brand name, either. To promote subject-based indexing requires imagination. The idea has been around for hundreds of years.
The third reason is ironic. Sometimes people choose not to use Topic Maps, not because topic mapping doesn't work, but precisely because Topic Mapping actually works. Of course, that's not a problem for you, because your organization actually seeks to maximize the productivity of the communities it serves.
-- This pitch won first prize, and was timed at 40 seconds. --
index of other writing by Steve Newcomb