I don't want to keep beating a dead horse, but my thoughts are that if people are going to try to compare it with real world computer operating systems to explain it away, then they miss the point. This is a film set in a fictional scifi universe. We don't need to explain that the computer does other things. We only need to see that it does the one thing we see it do - show the people on the other end of the line. Moreso, why does it even need to be capable of doing anything else? This is his meditation chamber. Somewhere Vader is going to be in isolation and only disturbed if absolutely necessary. It could (and due to that logic, probably should) be JUST a communications viewscreen and nothing else. I don't see Vader needing to monitor reactor levels in there, or compile the Empire's spending reports on Microsoft Excel.
Now don't get me wrong - having a HUD doesn't undermine it being just a screen either, and I very much like the look (though perhaps toned down a bit on the left), but people using the screen's other imagined functions, that we never see, as justification for it being there is tortured logic.
But if you want to continue with that train of thought and lets say that it was canon that his computer did other things, consider this: I'm on Google Chrome right now writing this post and I just hit f11 to put it into fullscreen mode. There's no taskbar, no address bar, it's the most elegant and minimalist way possible of having just what I need on the screen. Don't you think that in this futuristic universe there'd be a similar approach? Further augmented by AI that does so seamlessly as well?
Again, I have to reiterate that I love the HUD look. The frame gives it that scifi look and you can easily imagine the text on the right representing the video buffering. ;-) It's only the bit on the left that's intrusive as it gets in the way unfortunately.