I think there is (and should be) room for both commercial and open source projects to coexist for linux, that way there is always the freedom to make the choice about what to use depending upon requirements, ideology, financial constraints etc.
As a commercial developer, linuxDSP has had to go down that particular (commercial) road because we have significant costs associated with maintaining the infrastructure required to produce, distribute and develop the software, however, we started making audio software for linux, first and foremost as enthusiastic linux users - who just wanted to make some great tools to do what we wanted to do, and to bring them to a wider audience in a way that enabled us to continue their development.
That said, we realise that although our software and applications themselves contain no GPL'd code, they are indirectly dependent on many projects (e.g. DAW applications) which may be open source, and where possible we support those projects and - revenue permitting - hope to be able to contribute some financial support back to some of those projects too.
+1
The best example here, even though it has nothing to do with plugins, is Flash. I hate flash almost as much as Jobs and Stallman but the sad truth is that I still have to use the hunk o' junk or suffer a problematic or inconvenient web video experience. Yes, I know there will be a number of you who never or rarely watch streamed videos just as there are those who never or rarely use FX or softsynths but there are people like me who want all of these and want them working as well as possible under Linux *now* and are prepared to put up with non-free until the day arrives when a comparable FOSS solution exists. Hence, I fully support LinuxDSP's efforts, will likely be purchasing their plugins soon (long story still in progress..) and would do the same if someone released a real good LV2 softsynth if it was reasonably priced. Unfortunately I can't afford and don't have the room for lots of good hardware synths and as for Flash I think Linux's popularity would've suffered significantly if Adobe didn't support Linux (for Flash at least- I suspect Apple+MS pay Adobe not to port CS to Linux as too many would switch if they did a good job of that ;)