Where exactly is this on your iPad because it seems that I have something similar. Except mine might be a little bit wider, maybe twice/thrice as long?
Same story here though, I only noticed it because I was putting on the screen protector and wiped the screen clean to see if any dust got under the screen protector, and then I noticed that small line of pixels.
At first I thought it was a scratch on the screen protector, so I inspected it, and that wasn't it. I pulled it off to see if maybe it was a piece of dust, and it definitely wasn't. Strange thing is that it's definitely noticeable now when I'm browsing the web or using any apps with a bright background, I never noticed that before and I inspected the screen when I first got it. So it must've happened on it's own (??). I really don't know.
Anyways, it's not dead pixels because they change colors depending on my viewing angle. And out of curiosity, I put that line against a horizontal line on the engadget app when you have the list of stories, and if I change my viewing angle, the line moves away from the engadget app line. It's so strange.
Mine is on the lower right corner if you're viewing your iPad in portrait mode, with the Home button towards the bottom.