I didn't notice this until I took a closer look. The line makes the lower half of the screen more brighter than the upper half. I have the Xbox 360 version by the way. Is it my version of the copy, or all copies for the Xbox 360 versions like that, because none of my games are like that?
More seriously though, I'm playing the game on PS3 from a disc, and never saw anything like this. I've played a copy of the game (also disc-based copy) on a friend's XBox 360 and they never had a problem.
It could be that there's a problem with the TV, the HDMI cable, or some kind of weird compatibility problem. Have you tried forcing the game to upscale to 1080p? Or the reverse and locking it to 720p? I've had a few games which had major screen tearing issues when I was using a cheap HDTV a few years back, and when I locked out the 1080p option on the PS3 they worked fine. The game hadn't been running in 1080p, but for some reason, forcing the resolution they were already using fixed the problem.