Quarter of an inch away from the already bright screen is very different to quarter of an inch above the keyboard. Keyboard doesn't even register in my peripheral vision. Putting a changing, illuminated screen where it will be in my peripheral vision is a guaranteed distraction - as sense of movement and light is stronger in the peripheral than straight ahead. If you must put it there, put it above the FKeys so I can a) use controls how suits the context best, and b) disable the display when it suits.

As to why not just part of the main screen - well Apple don't want to go entirely touch on the main screen implying two different devices, and separated it clearly serves a separate, distinct purpose.