Well, OS X is easier because much of the work has already been done for Linux 64, as both are posix-ish lp64 architectures. Whereas Windows is llp64 plus its ow

Well, OS X is easier because much of the work has already been done for Linux 64, as both are posix-ish lp64 architectures. Whereas Windows is llp64 plus its own APIs and ABIs, which means much more unique porting issues. Beyond that, there's all the infrastructure you need to stand up for development, continuous integration, QA, metrics, and shipping to hundreds of millions of users. The logistics of that part are almost the same as supporting an entirely new OS, and in the case of Windows it's one with an insanely large and diverse population. So yeah, that parts actually a lot worse just because of the sheer numbers.