Quoted from neurokinetik:The idea is that you can display any pertinent information on the screen without having to have an obvious big rectangle in the middle that breaks up the art. The final effect being the information looking like it is being displayed right on the playfield.
Hell, one could take this a step further, by using a projector to shoot the info wherever you want it on the playfield, like a HUD. That's something I've never seen done before.
Right, I get that, and it's clever, but it's just not really pertinent to a game like Alien where you want to show film clips and full screen animations etc. I don't know what Nemo puts on that screen, maybe it's more minimal and so it's cool to keep a background behind it that matches the playfield.