Author's reply

> 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.

I thought that was the case. Good for Paul! When I mentioned it as a good example of a "commercial" free software project, I meant specifically a project that the main developer(s) seek to sustain themselves financially with, while remaining free software.