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 It was originally made as a caching layer for livejournal, and IIRC was made in the early half of the 00s.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.)
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.