interesting question. Sometime back I was wondering the same thing with my CDRW drives and Ricoh High Speed CDRW discs.
My old TDK 4800D (not liteon oem) writes to me Ricoh discs at 12x, but 52327S, 5238S and LG 4120B can only write to them @ 10x.
granted the difference in speed is not that great, but since the media is well capable of 12x write speed, why do the drive manufacturers have to set the limit at 10x?
LG GSA-H42N DVD-RAM (RJ11, auroreset RPC2)
BenQ DW1655 DVD-RW (BCIB, RPC1)
Noise Control w/ Nero DriveSpeed 3.06