I think what they mean is that accuracy affects your damage output in so much as it affects how many times you hit the mob. You do 5 attacks and if all of them hit you get 200 damage total, but if some of those miss you could end up as low as 75 damage.

Which is true. Aaaaand it's why accuracy is important. Also important if you're a tank as missing a part of a combo means less enmity as well as missing the initial pull with Tomahawk/Shield Lob.