You're absolutely correct that gzip compression will, in almost all cases, get you nearly all of the speed benefits minification will, and is generally a better method (and easier to do, as well). The reason so much JS, CSS, and HTML gets minified, in my opinion, is entirely a function of Google Pagespeed Insights. Regardless of the actual speed of your site, and regardless of the presence of gzip compression, if you have unminified JS, Google will recommend minifying it. They'll give you an estimate of how much you'll save, but even if it's low, the tool is generally used by average web users (ie, not true developers) who simply take Google's advice on its face.