For the most part, I'm pretty sure no one knows of parts inside of a laptop on the forums. Not really something most people tamper with. I could be wrong though
I've taken apart many laptops, including completely disassembling and reassembling my IBM ThinkPad T40. So, yes, you're wrong.

Anyway, that cable looks like it's for entirely controlling the monitor. It's used to control the backlight, and control what's shown on the screen (and possibly, if there are LEDs on the monitor for power, hard drive activity, etc. it can be used to control those LEDs as well.)
Most of the time, when laptops are made, they just run everything through one plug-in. It saves cost, and it saves having wires going all over the place, and it's easier to fit into the hinge of the screen, hiding it away nicely. Sadly though, the cable, like almost every other laptop, looks to be proprietary (meaning it's not going to work with any other laptop, only the same or similar laptop).