> Not like one would continually check out the latest version.

Why not? It's being updated regularly: https://github.com/necolas/normalize.css/commits/master

Because it's a reset file... meaning the moment you change it the changes will cascade into your css.

The last thing I would want is the behaviour of my css changing periodically.

Its not silly at all. It keeps version history and people can easily share their changes, and github provides an easily accessible place to download the file from. What would be a better place to share this file?