The green iSight light predates the unibody MacBook Pros. At some point they changed it from a visible hole to small invisible ones. Those laptops still had the sleep-light on the "opening button" in front (this button and the self-hiding magnetic latches were removed on the unibodies).
That bar is actually a series of those small holes to let the light through. The green light for the metal casing came later IIRC.