Well, that's right. The GPL is designed so that you can't copy-and-paste GPL code into a closed-source project. For software competing with each other, that stops the arms race being won by the side that can use their own work, and the work of the other side.
It is certainly fair in the sense that the Linux or BSD kernel people will never get to see, and benefit from the NT code, but microsoft and Apple can certainly use any BSD or MIT licensed code they want to.
But using Linux kernel code in the NT kernel is a special case of software sharing that can only be done at the source code level, by experienced programmers. And then it has to be released by the project maintainers, in this case the linux foundation, or microsoft.
But application code (e.g. an mp3 player), can be released for both windows and linux whether they are closed-source, or GPL.
The kernel might not be the best example to make your point.
It is certainly fair in the sense that the Linux or BSD kernel people will never get to see, and benefit from the NT code, but microsoft and Apple can certainly use any BSD or MIT licensed code they want to.
But using Linux kernel code in the NT kernel is a special case of software sharing that can only be done at the source code level, by experienced programmers. And then it has to be released by the project maintainers, in this case the linux foundation, or microsoft.
But application code (e.g. an mp3 player), can be released for both windows and linux whether they are closed-source, or GPL.
The kernel might not be the best example to make your point.