Blaming (or crediting, however you want to think about it) GNU for proliferation of Unix is anachronistic. RMS has repeatedly said he doesn't care for the design of Unix, but he chose it for the ease of implementation. GNU wasn't even bootable as a stand-alone OS before 1990s and certainly not production ready until Linux was. Using GNU utilities in proprietary Unices was popular, at least since the 90s, but I never heard anyone consider them a "killer app" for Unix.