Where did I say I didn't know Unix? The problem is that for some deployed solutions adding in Linux boxes simply because they host one piece of software isn't optimal, so "native" solutions are chosen instead. We aren't talking about a product that is tightly coupled with the OS (or at least it shouldn't be).
It should be, actually, if it's going to be fast. Memcached is fast because it optimizes interaction with the I/O layers -- you can't stay portable if you do that.
EDIT: Actually, you can use libevent for some subset of these cases and get speed+portability, but I'm pretty sure memcached predates libevent by quite a bit so they're not. So there's your answer.
Memcached predates github by quite a bit, actually. It was originally made as a caching layer for livejournal, and IIRC was made in the early half of the 00s. (Having a hard time finding an exact date, though.)
I have no idea what link you clicked on. The one above says this:
committing memcached
bradfitz (author)
May 27, 2003
Specifically, that was Tue May 27 07:19:11 2003 +0000.
I spent a long night back in 2008 recreating that history as accurately as possible. It involved a couple of git repositories, subversion repositories, and a lot of google and mailing list searches to ensure that every one who ever contributed to the project was properly recognized.
My apologies, and thanks for the exact date. I missed that the github commit date was in 2003. (If you miss that, your reply comes off as really snarky. Mine was a bit blunt, too.)