Consumer-grade DVD blanks can't burn dual-layers due to reflectivity issues (ie consumer-grade DVDrs, as with comsumer-grade CDrs, are less reflective than the factory-stamped ones. This is why some devices can't read CDrs or DVDrs). They also lack the area where the encryption info would be burned so that you can't do a direct bit-for-bit copy. If you were able to do a bit-for-bit copy, the MPAA couldn't come after you for violating the DMCA. The only way to copy a DVD now is to crack the CSS and then copy it thereby violating the DMCA.