Yeah, the word trade kind of implies that you're expecting something in return, hence the confusion. I would personally prefer all the bonus material in a folder as mp4s or mkvs, so that I can just put it on a BD disc alongside an mkv of the movie with the commentary added, which I want to make for myself but other may prefer something else. Another factor is that to create a DVD, you'd have to re-compress the already compressed files and so you'd downgrade them further, especially with MPEG2 DVD encoding.