​Ron you are right..   A number of us used dmr's compiler much less Steve's compiler to "port UNIX" to a lot of different things (some where good and some not so good - my own attempt at retargeting the V7 Rtichie compiler to yet to be name processed experimental process from Moto (later called the 68000) proved "good enough" for the Magnolia project at Tek but it was not really not a very good compiler).  But you had to have an AT&T license to get it.   Admittedly a lot of universities did and that did certainly cause C to get a huge foot hold over its contemporaries (say BCPL, BLISS and maybe PL/360).

IMHO: what rms did was put a production quality compiler into play that had sources, that anyone could use and anyone could hack on without having to purchase it or need some sort of license other than his GPL.  At the time, there had been lots of attempts at different compilers both "free" and commercial - some with sources some not (I fondly remember Ron Cain's Small C for the 8080 being pushed in Byte Magazine the late 1970s/early 1980)​.   Even Whitesmith's (Plauger's) compiler  was really not what would we have called production code quality.

gcc was not (still is not) perfect and compared to a number of commercial compilers -- say something like the current Intel compiler or the old DEC, Masscomp or Sun compilers.   But the "gcc family" did prove to be fairly easy move to a lot of UNIX/UNIX-like and non-UNIX OS platforms, at the same time able to be retarget to a number of different ISAs, even a number of different front ends; all while generally creating good/reasonable if not darned good/close to optimal code (at least for many of the targets were the most popular/that mattered).

Frankly, we have seen few developer suites that have been as lasting and I might suggest that until the LLVM project there has been few (none) that have had a chance of being so [Tannebaum's compiler kit maybe - but I never same that it never really went anywhere]. 

My observation is that without a "pretty good" compiler that was reasonably "universal" the rest of the command suite would have languished/not happened.   As Doug points out the base OS really never happened from rms (they had Trix, then the Hurd and finally defaulted to Linux).   But the command suite was able to grow and lots of people besides rms contribute to it, because the basic development tools were there.   As strange and difficult a person he is, I suspect we do all own rms a certain level of thanks for the basic dev tools.

Clem