It helped OS X ;-) OS X benefited from the labor savings of forking somebody else's existing project, dramatically reducing cost & time compared to a) continui

It helped OS X ;-) OS X benefited from the labor savings of forking somebody else's existing project, dramatically reducing cost & time compared to a) continuing to support OS9 b) starting from scratch. The technical nature of its status as a Unix derivative is, to my knowledge, basically nothing to do with its current market success. The Navy's practice of stripping old ships and building a new ship with the old hull comes to mind.