I just read a post by Amir today where he said optical discs elongate due to the constant spinning and that BR discs having a hard coat causes them to warp since the hard coat doesn't "stretch" the same as the other layer.
This sounds really fishy but wanted to see if anyone else had heard of this.
http://www.avsforum.com/avs-vb/showt...php?p=10848282
(he posted it at 2:18 but I don't know how to link to a specific post on AVS)