Part of my curiosity was sparked by the article on HN the other day discussing the hamburger menu icon: it used to be confusing, but now is pretty widely recognized as long as some guidelines are followed. So while I used to agree with you re: usability, these days I'm not so sure anymore.

One idle thought I had: when computer interfaces were still new, using physical analogies like file cabinets was good practice for teaching new users. Maybe GUIs are now commonplace enough that people are able to speak the different "languages" without as much trouble.