Digital data has standard formats. All the parts of the data "tree" need to be present, even if they are not used, so that the equipment can successfully read the disk. If parts were missing, the machine couldn't tell if that feature was not used or missing because the data was corrupt.
If it was an audio only DVD, there would be files in the Audio_TS folder. In a video DVD the audio is with the video data.
You ought to see what data is transmitted to make digital TV work!