Pure's stylesheets are already minified, the only result of re-minifying them is that the copyright will be removed: http://yui.yahooapis.com/pure/0.2.1/pure-min.css

I squash all my stylesheets into one giant .css file to serve rather than a bunch of individual stylesheets. A side-effect of squashing + minifying (which is done every time I generate my website) is that all comments are removed.

You are correct, that notice is not present, but I did not remove it intentionally. To be honest, I didn't read the LICENSE.md of Pure CSS. Shame on me :)

Feel free to file a bug against this at: https://github.com/ryanseys/ryanseys.com

TBH, I don't think you're in the wrong here, but expecting someone who has already brought something to your attention to file a "bug report" against your personal website is a bit arrogant.

Fix'd. https://github.com/ryanseys/ryanseys.com/commit/2c043f