So no one has comments on the original question per se, which is about dual licensing ("free" or $$$$, depending on who's using it)?
I don't know if you are changing the question, but free != Open Source. Of course, Open Source can be used commercially, and a license that specifies usage restrictions depending on user is not Open Source. (It is a fundamental principle of Open Source that same conditions apply to all licensees regardless of field of endeavour).
There seems to be a common myth about dual licensing that it is a way to force commercial licensees to pay for using Open Source code, but it can't work like that. Once you add a "non-commercial" restriction, it is no longer Open Source. You are just offering two different non-open licenses. ie. You can have a license that says "free but only for non-commercial use", but there is no recognised Open Source license that allows that restriction.
With dual licensing, you can induce commercial licensees by relaxing requirement to publish source code (if GPL), or by providing better support, but the commercial licensee still has the option to use the Open Source license. With an LGPL license or BSD, the commercial user would not have to publish code, maybe just put a credit in the documentation.
So is the question about free software or Open Source ? The answers are quite different.