> artists earn money by performing
What you're saying, in economic terms, is that musicians have rivalrous, excludable goods they can produce: the concert experience.
That's not bad, although it would have the IMO negative effect of leaving the Brian Wilson (much more oriented towards studio work than touring) types between a rock and a hard place.
Authors don't really have that: they could sign books, but that would reduce their income drastically, as most copies would be freely had.
> Open source developers earn money by utilizing their knowledge and skill in paid-for projects.
As for the open source developers, but WHERE DOES THE MONEY COME FROM in those paid-for projects? Scarcity is where it comes from, and often, they're getting paid to work on open source by someone who deals in the artificial scarcity of intellectual property.