I would be surprised to find anybody doing serious development without relying on open source software somewhere.
And the companies I've worked for have generally been very willing to release code as open source, partly for goodwill and advertising (we've received several job applicants who only learned about us through our contributions to open source projects), and partly to avoid the cost of maintaining an internal fork of, say, Boost or JQuery. Even if you can't open source the whole kaboodle, it's often possible to release something, especially additions to existing open source projects.
free software to me does not mean free for all. a person and an organization can still keep its secrets. (corrections welcome)
So, in your hypothetical, it turns out to be very hard to prevent the distribution of the source, unless all the POS units are held in-house (that you are a company developing and using your own POS units in commerce, as opposed to being a POS vendor) and that all your employees who have standing to receive a copy of the source have some compelling reason to not distribute it.
That's a feature to GPL advocates and a bug to GPL detractors.
I wasn't trying to tell people how to be Stallman's friends, or how to get absolution (for whatever wrongs) by following the FSF's advice. Instead, I want to encourage people to pick their battles. If you can't get permission to release your full program as open source (or, if you plan to become rich and don't see any way to do so after you've published your source code), then perhaps whoever is responsible for the decision would be willing to release less than everything today.
I disagree because this is HN
Please re-read the site guidelines: https://news.ycombinator.com/newsguidelines.html and https://news.ycombinator.com/newswelcome.html.
No need to be condescending. I've actually been researching this a fair bit lately for a new project.
What I found was that even though people parrot the revenue models you list above, the reality is that it is far more risky to go open than to "control the supply".
The margins on services (consulting, training, support etc..) are much lower than selling the code.
Here is one example I came across showing how it's no slam-dunk: http://www.locomotivecms.com/articles/we-tried-to-solve-the-...