The sad reality of being an individual who creates (be it music, books, stories, films, etc.) is that if you're not careful, there are literally millions of ways you can lose the rights, and more importantly, the royalties for whatever it is you've done.  Recall the sad fate of Bill Finger, the co-creator and writer of Batman (and the man who came up with much of this famous character's lore), who died poor while Bob Kane, the artist of the strip (and most certainly the character's co-creator), received all the credit and fame for Batman's creation.

Robert Heinlein, certainly a famous enough author in his own rights, created many wonderful science fictional concepts, many of which were "borrowed" and showed up in other works and movies, without Henlein being recognized for his contributions (ever read Heinlein's The Puppet Masters?  Curious about its similarities to Invasion of the Body Snatchers?  Heinlein's book was first published in 1951.  Invasion of the Body Snatchers (the book by Jack Finney) was first serialized in 1954 and the first film version was released in 1956.  By the time The Puppet Masters was made into a feature film in 1994, I recall at least one critic mistakingly feeling this film was a pale "imitation" of Invasion of the Body Snatchers!)

Similar things happen in music, but in this case, organist Matthew Fisher is getting his due (credit and cash):

http://www.cnn.com/2009/SHOWBIZ/Music/07/30/procol.harum.royalties/index.html