>Open Source provides a way for some authors to publish software optimized for quality
This is literally true because of the word "some" in there. But if you mean that it especially leads to quality, rather than just "some quality happens", open source programs are notably deficient in many ways. Programmers don't like writing and don't need documentation for their own program; are familiar with the program's functions so they don't need a good UI; and they have different needs from average users, so their programs may not meet those users' needs very well. Whether you want to call that quality is, I suppose, up to you.
Yes, I was very deliberately not generalizing to all of Open Source. I was exploring these assertions:
> It's not true that just because a product is open source, it will be of good quality.
> [...] it does appear to be true that at the extremes, the best quality software delivery processes are from open source projects.
To turn around your argument, I think your generalizations about "programmers" are too pessimistic. Many of the best Open Source authors enjoy designing good user interfaces and writing good documentation because they want to make something awesome and beautiful. And commercial entities generally won't/can't give software developers free reign to do that because of marketplace pressures to optimize for profitability and value (which are awesome and beautiful in a different way).
This is literally true because of the word "some" in there. But if you mean that it especially leads to quality, rather than just "some quality happens", open source programs are notably deficient in many ways. Programmers don't like writing and don't need documentation for their own program; are familiar with the program's functions so they don't need a good UI; and they have different needs from average users, so their programs may not meet those users' needs very well. Whether you want to call that quality is, I suppose, up to you.