Well, the link you gave simply gave a subjective score without any image shots to back up the scores. It just showed a results graph that gave the appearance of ATI being better without actually showing what was better. I'd hardly say that makes ATI better than nVidia for viewing 2D movies. That is mostly going to depend on the monitor/tv and the software used with modern graphics cards these days as they are all (both AMD and nVidia) deliver good quality.
That article used a discrete ATI card, btw. Hilbert simply listed a few IGP's as they are capable of good video playback, just not quite a good when you start using more advanced functions. It may be older, but nothing has changed which is why it hasn't been updated.
Did you just call HQV tests subjective? Seriously? What does that make the GURU3D article then, even-more-subjective? A no-show, since it didn't even try to compare IQ in an objective manner?
The GURU3D article was mostly written as a how-to guide for MPC-HC. But when it came time to compare GPUs, it was mostly comparing IGPs, with a discrete card thrown in as a point of reference. And all of those GPUs were old. The OP here is not trying to optimize MPC-HC or to compare old IGPs against each other; he wants to know which of the latest discrete cards have better 2D video playback. Totally different questions!
I agree that TV/monitor and software could affect IQ as well, but I think the appropriate phrase is "ceteris paribus." That is, on the exact same screen and software, which video cards tend to do better in 2D video playback?
Let me put it this way: imagine we are discussing audio instead, and he is talking about speaker quality. Imagine AMD and NV make sound cards. You are saying that maybe the receiver, AV cable, speakers, etc. have a bigger impact on overall audio experience than the sound cards do. That may be true, but that doesn't address OP's question, which I have interpreted as: holding ALL ELSE CONSTANT, which sound cards are better, the AMD ones or NV ones? (I may be misinterpreting his question, but I think the assumption implicit in his question is that you hold all else constant.)
For people with insensitive eyeballs (for lack of a better term... you know what I mean, I think), the overall viewing experience might not be that badly affected even if one video card has worse video playback than the other; in fact, a sufficiently insensitive eyeball would see no difference in quality. But even if that is true, it doesn't change the fact that NV has inferior 2D video playback right now. It's subjective just how inferior they are... maybe it's only slightly inferior so OP would never notice the difference anyway, just like how I (with my insensitive ears) can't really tell the difference between high-end and ultra-high-end audio.
But I know some people are very touchy about trying to get the best. That's why some people shell out small fortunes on A/V cables that give just a little bit better performance, for instance. Or even bigger fortunes on slightly better speakers, etc.