i have to disagree.
while i'm not speaking with any authority or any official knowledge, i feel that the strength of the polycarbonate plastic of which the CDR is made is not the issue. after all, many are reading 12x rated CDRs on new drives at 52x and "exploding" CD occurences aren't that common.
i believe it has to do with the dye.
e.g. Verbatim/Mitsubishi media: up to 16x they used Metal Azo, with newer and faster media they switched to Super Azo. my conclusion: the Metal Azo couldn't handle being written at faster speeds.
probably has to do with the fact that when burning at a higher speed, the laser has "less time" to burn the "pits" onto the CDR, the chemical reaction of the dye due to the laser heat has to be quicker.
One Ring to rule them all, One Ring to find them,
One Ring to bring them all and in the darkness bind them
In the land of Mordor, where the Shadows lie
M.C. Escher - Reptilien