Remember, most Unix vendors charge more for their systems than Windows vendors, and full-on Unix-based solutions are costlier than Windows ones. Virtually all of the examples you are citing come from academic computing - Unix is more respected in academic CS environments, and academic projects are more likely to be released freely. GIMP, Postgres, Linux, BSD, Mosaic and Tex all had roots in academia - the only major open projects I can think of that didn't are Mozilla (which, remember, has some roots in Mosaic) and Apache (which also began life, I think, in the original NCSA httpd, although I may be wrong.)

You want to promote high quality free software? Promote higher education! Make it more exciting to work in academia than in the private sector!