there are some issues with the screens that I'm not happy with... I have a mbp unibody... there is an area near the center that is decidedly less bright than the areas around it.
Also damage from pressure on an LCD screen wouldn't manifest itself the way you describe unless it was currently being put under pressure. If you put your finger on any LCD screen and apply pressure you will see varying degrees of color change, but unless you actually rupture or damage the cells the liquid are in, those color changes will go away as you remove the pressure... and if you cause damage to those individual cells you will know it and there will be no doubt.
I think the reality is the LED backlight technology isn't perfected at Apple and some of us are getting the apple bleeding edge misfires.
Good luck with the apple techs, let me know what you find out. I would have taken mine in long ago except the flimsy shell got a dent in it before I could find the time to drop it off... now I'm quite certain they would simply claim the dent had somehow caused it ignoring the fact that the dent is in a completely different part of the screen as the dark area.