Linux kernel copyrights
I wonder if that choice of letting everyone hold individual copyrights instead of signing them over was by design from Linus. He has never seemed to be overly bothered by people copying code from the Linux kernel into proprietary products, at least not the degree that Hellwig and certain others are, let alone the FSF.
Linux might not have reached where it was today if copyright had been assigned to the FSF, and there had been a few high profile lawsuits that made large companies back off. Even if they weren't intending to misuse the code, just the worry about accidental misuse causing exposure of their proprietary IP would be enough to dissuade some. Who knows, maybe Android would have ended up based on FreeBSD. Not that I think that would really make any difference to Android, but getting Linux on a billion devices worldwide certainly has helped increase its reach far beyond what anyone would have thought possible 15 years ago.