I don't think that's a fair comparison. OS X doesn't rely on Windows developers to make it better, Ubuntu needs other developers from across the Linux community

I don't think that's a fair comparison. OS X doesn't rely on Windows developers to make it better, Ubuntu needs other developers from across the Linux community to get better. You can't really do "closed" Linux, because you (the closer) need everyone else. And, as seen with Intel's rejection of a mir patch, everyone else can shut you out.