Indeed. The best approach is to have DVD Decrypter extract the program as a single VOB in IFO mode, using the option to only include the streams you'll be needing: the video and whichever audio track you want to preserve. If necessary, you can simultaneously have the software redesignate the audio track to 0x80. The resulting file can then be renamed with a .mpg extension.
I still have problems with files like this afterwards, though: if I author a new DVD using such files directly, very often playback chokes. There's something about the header of these files that results in incorrect bitrate readings being passed along to standalones. I usually, therefore, have to run a reencode pass at the highest bitrate the project can handle. but there must be a better way to fix this problem.