http://www.cdfreaks.com/article/113

其中個人認為比較重要的是這段
Another bad side effect of this pre-pits method is that DVD-R(W) mastering is made more difficult than with DVD+R(W), since a higher precision is required to cut both the grooves and the pre-pits between them. Special dual-beam recorders are usually required for - stamper mastering, although some manufacturers now also use single beam cutting.
Not only are the pre-pits more error prone than phase modulation, but data they carry are also less protected. In one ECC block pre-pits carry 192 bits of information (one pre-pit block). Out of these 192 bits, 48 are not protected by any error correction mechanism, 24 bits are protected by 24 bits of parity (A parity), and the last 56 bits are also protected by 24 bits of parity (B parity). All in all, this strange heterogeneous structure finally gives a pretty weak protection to the information bits carried by pre-pits.

有說明DVD-R的ECC是比DVD+R不完善的...