Hmm.. that leads to a couple of random thoughts:
1. How up-to-date and comprehensive does it need to be? What kinds of queries will people need to access (either directly or indirectly) about music, to serve their purposes?
2. DBPedia, through Wikpedia, actually does have a lot of information about bands and musicians and music. For example, see:
http://dbpedia.org/snorql/?query=PREFIX+dbo%3A+%3Chttp%3A%2F...
3. But Wikipedia will never be comprehensive exactly because of their notability guidelines. All the latest new super-underground Norwegian Black Metal bands that are recording in a wood shack in somebody's backyard, are not going to have Wikipedia entries.
4. On the other hand, musicbrainz.com seems to have an awfully comprehensive set of listings. And their data is part of the semantic web / linked data cloud, as well.
By way of example, Verminous are something of an underground act, and are not on Wikipedia, but their info is in Musicbrainz.
Anyway... just thinking out loud here.
Facebook have also become a serious problem, in that a lot of places publish there without realising or caring that their information essentially is locked in. This gives their graph search a simply enormous advantage over anyone else.