1. I believe only PAL DV is 4:1:1. NTSC DV is 4:2:0. Or it's the other way around; I can never remember. But they're different.
2. Feature films are also often stored as log formats, so that there's more gradation in dark areas and less in light ones. Or it's the other way around; I can never remember. But it's not linear, anyway, like all the consumer YUV/RGB solutions we're using. Don't ask me to explain how that goes, exactly.
3. You can work in Photoshop in LAB colourspace, which is (I believe) almost identical to YUV. It's set up the same way, anyway: independent luma and two chroma channels. That lets you do stuff like blur stuff in one channel (let's say luma) without messing with the colour. Very handy for smoothing out skin, for example.
4. From what I understand, the gamut of YUV is smaller than that of RGB. Of course just how smooth and effective each colourspace is depends on sampling rates, etc., but in general RGB can display more colours than YUV (e.g. a whiter white, or pinker pink). Which I imagine is one of the reasons working in RGB is the default method for computers.