Are there more people releasing drivers for Linux 2.6 or 3.9 (the versions released ~when Win 7 and Win 8 launched respectively)? Or for OpenBSD 4.4?

I think the state of support for Linux and open source in general is much, much worse than for commercial software.

No one is maintaining >10 year old software. Especially not for free.

Do note that this is not a story about not being able to run Win 7 anymore - it's simply about having it more difficult to release and install new drivers on it.