I do assume that. Linux rapidly caught up with the BSDs despite their huge head start, which demonstrates the industry does have a critical mass of developers who are willing to contribute their work rather than go through the pain of tivoization or building from scratch.
So, its my understanding, that this wasn't do the GPL versus the BSD license, but had more to do with the uncertainty hanging over the BSD distributions due to a lawsuit threat from proprietary Unix.
Now of course I could be wrong, but I think there may be other factors which could explain the difference.
