Remember, most videos (even NetFlix) are highly compressed videos. Because they are highly compressed they do show compression artifacts and those compression artifacts are seen as "crushed blacks," "dancing colors," macroblocking, and other forms as well.
Because a lot of videos are what is referred to as "bit-starved" the video codec that is decompressing and rendering the video has to fill in parts of the video that were taken out during the compression phase. This process isn't at all perfect and unless you are looking for it, most of the time we won't notice them.
Myself, I'm a bit of an HDTV snob. I can see where video has been compressed too heavily by the broadcasters and cable companies. Annoys the hell out of me that I can't get the perfect picture that I would get if I was watching a perfectly encoded Blu-Ray.