Modularity and FOSS
This article raises some interesting points about MySQL/Postgres example. Is Postgres more modular than MySQL? I'd really like to know the answer that question.
Perhaps, building off Chopra and Dexter's description of FOSS aesthetics, we can come up with a different theory. For example, maybe there's a strong relationship between "good" code and open or visible code. Perhaps people who know they are writing for a larger audience write better. I think this is supported by my own anecdotal experience that the major reason that people don't release work freely is because they are not confidence in the quality of their products. In that sense, maybe it's the visibility rather than the actual form of engagement? That would be a pretty interesting result.
MacCormack, Alan, John Rusnak, and Carliss Y Baldwin. 2006. “Exploring the Structure of Complex Software Designs: An Empirical Study of Open Source and Proprietary Code.” MANAGEMENT SCIENCE 52:1015-1030.
MacCormack, Alan D., John Rusnak, and Carliss Y. Baldwin. 2008. Exploring the Duality between Product and Organizational Architectures: A Test of the Mirroring Hypothesis. Harvard Business School http://ideas.repec.org/p/hbs/wpaper/08-039.html (Accessed October 16, 2008).