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).