I'm not sure why I feel like we're arguing over this; maybe it's because you believe with 100% certainty what your engineer told you, and that's fine. But honestly I believe that the "dust / stains / smudges" are in fact all part of the same problem, just described differently by different people.
Have you taken a close look at the "dust" in this one photo?
http://forums.macrumors.com/attachment.php?attachmentid=287668&d=1306956612
Do you see how it looks splotchy/smudgy? I could absolutely see how some people would confuse this for a water stain. In fact, look at the first comment from user "iammike1" on top of the thread I posted before:
http://forums.macrumors.com/showthread.php?t=1101370&page=2
He writes: "Mine wasn't dust. Was kinda difficult to wipe off. Almost reminded me of water stains which I guess could be possible if condensation got in between the panels."
So, I'm not saying it's dust, it might be some fine particle from something that was melted/separated inside the display as a result of the heat. But what I am saying is that people are able to wipe this off, albeit not always easily. My point in all of this; the "moderate" cases I've seen do not appear to be permanent damage to the LCD's but are clearly beyond the ability of an average user to clean, and will void an active Apple warranty if the screen is disassembled anyway. That's a far cry (to me) from what the kind of damage your engineer was describing.
I'd appreciate a little less condescending tone if you'd like to continue this discussion. I'm not the enemy here, nor am I a child or a complete stranger to the problem that has been plauging my iMacs for the last year or so.