The charts used in the Clarity are of a fixed resolution. At that specific resolution, they're nice and sharp, but you don't get much on the screen. If you want to zoom out (or in for detail etc), they become blurry as they're rescaled/resized as opposed to vector maps which scale correctly with no loss of resolution.
Think of it as zooming in on a cell phone photo. Looks ok on the phone, but zoomed in on a PC monitor it goes horribly blocky.