Yes. Sometimes those day jobs are working on free software, either for internal consumption or for clients. Say the company I work for need a Frobnitz added to the gcc compiler in order to do some task or other. I get paid by my company to add the Frobnitz for our internal business reasons and then contribute the changes back to the maintainers who can then incorporate them into a future gcc distro. My company has gotten what it needs, I've gotten paid, and the gcc user community has a new feature. This is how most of this stuff gets done.
Other folks consult and do customization of free software for a living. Stallman likes to think about a business model of programming more like practicing medicine than building stereos (but without the licensing guild). In medicine, nobody owns the expertise that is a physician's stock-in-trade and nobody really has a monopoly on the knowledge. Were it not for licensing, anyone with the desire to educate themself could practice medicine (at least on their own body). Physicians make money not from proprietary knowledge, but from expertise in freely available knowledge.
Stallman says programmers should get paid for consulting or whatever, not from licensing IP. The analogy with Medicine is not perfect, so don't bother picking it apart. Also, don't confuse drug or medical instrument companies with physicians. The drug companies are more like computer manufactures, not software producers, if you want to stretch the metaphor a bit further.
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Joseph Noonan Houston, TX jfn1 at msc.com