Yep. There is no "Linux Operating System." There's the Linux Kernel, and that kernel is used in tons of different OSes. It's sounds like a small nitpick but its a huge deal and a common misconception for those outside of the Linux world anytime a topic of unifying something in the Linux world comes up.

A shared or central wiki sounds nice, but could quickly end up too messy. Arch having its own makes sense, as in the case of Linux - the distro is the operating system. Arch is a different OS from Fedora, which is a different OS from Ubuntu, etc. Sure, there's a lot of overlap but they are each their own unique OS.