Well, the fact that it's not tweakable. That you can't set an expiration date on the cache. That you can't select what you want to cache. (images, video, CSS, js, etc)
I think the 'Developer_tools#Purge_all_caches' refers to the internal file caches that moodle builds up for speed.
Browser-side caching is different. You are telling the browser what elements it should cache and for how long it should cache it for.
These two caches are fundamentally different, though I appreciate the effort.