Well, that is the only reason why UNIX won and we got stuck with C, it is hard to win against free beer with source code available.
The prices that Bell Labs was allowed to charge for symbolic UNIX licenses were a gift, when compared against traditional commercial OS prices in the 70's.
One more advantage was that C and UNIX were designed for portability. They started on PDP-7 and spread onwards from there.
VMS was designed to sell mainframes so your choices were limited outside of that until the pedestal and workstation market arose around 88 (Alpha), MicroVAX, etc. Even then it was only DEC hardware. That's how you kill an OS.
There were already portable systems outside Bell Labs back then, and anyone that has written UNIX software knows how "portable" C actually was back then.
Had UNIX been sold with a price tag similar to VMS, without source available for universities to play around, and it would have been long dead by now.
Unix in the 1970s was completely irrelevant to the context of the article. I don't know to what extent we paid separately for the OS, but we had source for at least MVT/MVS and OS4000, of ones I used, which we didn't later for SunOS.
The prices that Bell Labs was allowed to charge for symbolic UNIX licenses were a gift, when compared against traditional commercial OS prices in the 70's.