My thoughts are that the offending .mpg's were part of a mass download from a FTP site because of the way they are organized. (Remember that DW had a cable connection.) The got put on a CDR during a routine backup.
What is more telling to me is that the media player record did not show them being played recently. It may be that DW did not even know they were there.
It is also telling that the CD case that contained them was never fingerprinted so that one would know who used the CD. We are left to assume that DW viewed the porn when in fact it could be a plant. I could make the same CD on my computer over 100 miles away and plant it and to the unknowing it would appear to be DW's.
Neal testified to finding the cd's and disks himself hidden behind the books on the shelf right where police found them.