Two major upheavals shafted a lot of audio engineers.
One of the most popular DAW suites is a package called Logic. After nearly twenty years of development, Emagic sold out to Apple and Apple decided to abandon the PC version. Suddenly guys who had used the same piece of software all day every day for a decade or more were faced with either buying at least one top-end Mac, having to learn to use OS X and potentially a whole bunch of other software, or abandon their preferred DAW and have to relearn how to do their work in a different DAW. Either option would prove enormously expensive for a lot of engineers, both in direct costs and lost work.
When Apple shifted over to Intel, there was a huge lag from many developers in getting updates released. For engineers, this is a serious problem - having the fastest hardware and the latest software is a significant competitive advantage. A lot of people lost out on work, or had to buy PCs or new audio hardware.
The experience of that world has led to my current position. Professionals in all sorts of disciplines have huge personal investments in particular software and are often completely betrayed by the developers. EULAs are a one-way street and only the most rarified of enterprise software has any sort of reciprocal commitment. What Stallman talks about isn't purely abstract. Relying on proprietary software is dangerous, for very straightforward practical reasons.