Even 24x, 32x and 48x speeds are stretching the boundaries of a technology that was orginally intended merely to play audio CDs at 1x.
Remember the excitement when double speed and then 4x drives were released and even more so at 8x; the prices too were astronomical. Then people became blase about the subject and accepted higher and higher speeds with little reaction.
As Gongoozler rightly points out, experiments have shown that disks can shatter at very high speeds, although it is pretty rare.
No doubt we will soon have DVD rewriter speeds escalating quite dramatically - meanwhile manufacturers will continue to overcharge customers for technology that has its basic roots in the humble CD drive.