21:9? 7:3? No, 64:27
They chose 21:9 to make it comparable to 16:9 (same denominator), but the panel has 2560x1080 pixel, which makes it 64:27 (or 4:3 to the power of 3). Remember, 16:9 is 4:3 squared.
This TV is great for people who watch a lot of movies, but don't want to install a constant height projection system. Basically, it gives you "constant height" in LCD form, which we did not have before.