So, Karoly is proposing that we test on MySQL, then throw the issue over the fence to the folk who use (and care about) PostgreSQL for them to handle, because of the INSTALLED BASE issue, and the TESTING RESOURCES issue. This is NOT a technology issue.
The previous analogy of Windows is incorrect.
A more proper analogy is : "I test on LAMP, because that is what I use. If others want to make Drupal work on Windows and IIS, then let them test there, and propose patches that do not put Drupal through hoops to support that. We are not specifically excluding Windows, and in fact some people use Drupal just like that".