> the browser should use the cached object without making any requests.

That's a common (mis)assumption, but that's not how it works in practise. Sorry ^^

I cannot comment on what was the intended behavior when HTTP caching and headers were first designed, a very long time ago.

It seems to me, that is was "request everytime + get 304 if not modified, thus save the file transfer time". That's how most implementations work in my experience.

Historically, transfer duration was way more problematic than latency. It's only recently that there are pages with hundreds of dependencies.

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Rails and webservers: They MUST change the filename or the application will be fucked because of caching issues, mostly because of Firefox :D