TV manufacturers stuck in the analogue past
Firstly, I *hope* they're 1920x1080 (or 2520x1080, or - more usefully - 2560x1080). Unlike LG's ultra-widescreen displays (which were even wider):
If they've gone with non-square pixels or a sub-HD 1920x823(ish), there goes the quality again. Of course, they have to call it 21:9 because 16:7-ish sounds like it's inferior.
As Bod says, any kind of scaling screws up the image anyway - hence my hatred of 1366x768 panels and TVs that won't let you turn off the overscan; I can't understand why an entire industry is so happy to throw away image quality. The ironic thing is the fad for anamorphic lens attachments for projectors - first scale the 2.35:1 vertically (digitally) up to 16:9, then stuff an anamorphic lens on the front to make it wider; a spectacularly about-face way of getting an expensive blurry image...
Re. 16:9 monitors, I agree they're stupid. For fitting most documents on screen they're too non-square - fill vertically and you have big borders horizontally (not, as suggested, a stretched image). A 1920x1080 monitor is *not* better than a 1920x1200 one, and it's debatable when you come to a 2048x1152 monitor (which at least has more pixels than WUXGA). On a CRT the aspect ratio of the monitor is arbitrary, but nobody thought about the numbers which come out for doing computery stuff with such an odd-ball aspect ratio. 16:10, which is at least half the standard SXGA aspect ratio, is much better.
God forbid that anyone would think that sticking to some kind of standard might be important. I'm waiting for people to start producing adverts with black borders top and bottom on 16:9, in case they're viewed on one of these.