Instructions for 10.3 and above are leaving out the Mount and UnMount steps that must be preformed before this will work. Also, when it comes time to eject the source DVD, you can't, because it is in use, so you have to close Disk Utility, then eject the DVD from the SuperDrive, then start Disk Utility again, then select the .cdr file, then Burn.
Disk Utility, OS X Mountain Lion (10.8.5)