No, it most definitely does not does not.
> There's no Expires header being set, so your browser is not caching these images.
You're out of your mind, of course the browser caches it, the browser caches everything it can by default: http://i.imgur.com/hrmIs.png
> A full roundtrip to the HN server to get back the "content hasn't changed" status code (304) is required for each.
That is not even remotely close to what happens in the actual reality we're part of.
No, it most definitely does not does not.
> There's no Expires header being set, so your browser is not caching these images.
You're out of your mind, of course the browser caches it, the browser caches everything it can by default: http://i.imgur.com/hrmIs.png
> A full roundtrip to the HN server to get back the "content hasn't changed" status code (304) is required for each.
That is not even remotely close to what happens in the actual reality we're part of.