<p>I wonder why no browser out there has such simple but essential feature. Am I missing something? Is there a technical reason?</p>

<p>I'm tired of all those javascript/flash/java hacks out there ...</p>

You have to post back to upload a file, regardless of whether or not you are being "sneaky" about it (using hidden iframes, for example); the browser's own progress bar (usually down in the status bar) is the file upload progress bar in that sense, although not exactly.
It's just that you can't easily use that data for yourself, so you have to approximate it with a lot of client-to-server communication tricks.