It's pointed out in the comments on that article that left-right aiming is a lot easier than up-down aiming, too, since left-right aiming depends only on being

It's pointed out in the comments on that article that left-right aiming is a lot easier than up-down aiming, too, since left-right aiming depends only on being able to line your arm up with the board, while up-down aiming requires you to correctly calibrate your throwing speed.