Free software and open software reducing your costs in making products that make money. Be they services (a la Google/Facebook), hardware, operating systems (a la Apple and Darwin), or books (a la OReilly), or consulting (a la IBM).
Open source itself doesn't make money.
So if you can open source and reduce your maintenance costs of something that is required for your product but not really a differentiator it is a win.
If you try to make money from open source itself, either you will fail, or else you will end up either de-facto abandoning open source, or else doing shady legal things to get around it (see the example of Red Hat/IBM in the article).
I am curious as to what you're selling, and why wouldn't anybody just download a free copies from somewhere else?
I've tried to build a community where supporting the continuous full time development of the software is seen as a social good, and thus worth participating in even if the software itself is available at no charge. Most of our income comes from "subscriptions" which have nothing to do with the licensing-style arrangements seen today, but are merely a recurring payment agreement that gives us a consistent income, allowing us to avoid endless "got to make a new release" mania.