If they cut out the audio you lose a major component of the video's character...I hope they clarify this.
Try to imagine what would Star Wars be without its music...
I agree as audio is a big part of my videos, but everyone has different tastes in audio and videos might be edited for different purposes. For example, entertainment vs. selling a product.
They responded to my question about audio by referring the youtube copyright terms and conditions.
Have not seen any further information on why they need the actual video files.