When I heard RMS speak a few years ago, he made the distinction between devices like microwaves, and general purpose computing devices. The latter you want to be running Free Software. But for the former it's not really an issue.
Unfortunately, the line between the two is blurry at best. For example, I'm not sure how well this jives with the case of the printer software which provided the catalyst for RMS starting the FS movement in the first place.
From the abstract: "...In particular, we consider programs for microwave ovens, which provide a basic open API for controlling cooking times..."
The authors were only able to _simulate_ a microwave oven, presumably because the software on real microwave ovens is closed. A reasonable argument could be made that the proprietary nature of microwave oven software has limited innovation in this market.
Think of it this way, the printer itself probably has some firmware in it. That firmware source code isn't as important as the printer driver, which is what allows you to use the printer from a general purpose computing device. Without the driver, the printer is useless.