In future articles I will take your advice re: proprietary vs. commercial. The distinction is valid and important.
You wrote that "I believe Ardour is a commercial project for the main developer" and you are close to the mark. IIRC Mac users can purchase a ready-made binary for OSX or download the source code for free and build it themselves (apparently a non-trivial task, considerably moreso building for Linux). Linux source code and binaries remain free as in FSF-defined free. A Windows version may someday appear, my guess is that it will be available a similar fashion to the Mac version.
The chief developer, Paul Davis, relies on user contributions to keep the project going (it's a big project), but Paul intends that Ardour will always be licensed under the GPL. You will never need to purchase the source code.