They're not really DARK lines or anything. Just faintly dimmer than the others. It's so subtle that you don't notice it unless you have a frozen vis that's made of mostly smooth white pixels. Attached is a .GIF file that approximates what I'm talking about.

It looks like the kind of thing where one might say "Oh, that's just normal for that kind of display". It's been there since I got the unit, so it's not like it's something that's cropped up recently or anything.

Look at the .GIF file and tell me whether your display looks like that.