I think you overestimate how much Sun controls MySQL. They have not made anything closed-source, and the stories that they were considering it a couple months ago were quite misleading. I think you're overestimating this in general actually. PHP is certainly not controlled by a company, and Fedora is a very open project.
Would it be any better if the top contributors to Postgres left the project than if the MySQL ones did? Unless you have some data showing that one project has a much more centralized group of contributors, I don't think you can draw any conclusions based on who makes money from it.