What I said was that the issue of printer drivers contributed to the GNU license. Not that it was the sole reason. And regarding the issue of Linux an printing it's worth noting the long history of printer driver problems.
Now regarding Stallman and printer drivers note the following wikepedia entry about Stallman's time at MIT which I have heard from the horses mouth many times:
In 1980, Stallman and some other hackers at the AI Lab were refused access to the source code for the software of the first laser printer, the Xerox 9700. Stallman had modified the software on an older printer (the XGP, Xerographic Printer), so it electronically messaged a user when the person's job was printed, and would message all logged-in users when a printer was jammed. Not being able to add this feature to the Dover printer was a major inconvenience, as the printer was on a different floor from most of the users. This one experience convinced Stallman of people's need to be free to modify the software they use.