Dear Sir, I can confirm that this fault is normally caused by physical damage to the device. Nearly every single device we have repaired with this fault has had some form of physical damage that has led to the fault. Of course the few that haven't were repaired under warranty. I quote directly from our repair centre: This issue is caused by air/liquid entering the LCD layer, and is nearly always OOW (Out Of Warranty) as it can only be caused by excess pressure on the screen. As long as you look after the device, and take care of it, this issue is unlikely to affect you. We have numerous Touch Dimonds here in our support centre, around 3 or 4 for each language we support, and not one of them have displayed this issue.
So I hope to find out with this poll how many people really have got this issue, respectively how many of them can explain it with too much pressure.