Well thats because DVD are out! The whole point of clips4sales is to download right now, why wait! And people can always burn their clips into CD Roms or DVD-Rs.
I stopped marketing DVDs a long time ago. I only do DVDs when a client requests it by e-mail.
I looked at your clipstore and noticed that you have big gaps between updates. That might be a reason for the lack of sales. My recomendation would be first try to have one clip per day, before posting more than one in one day. When you have enough material to cover every day then start updating more than once a day.
A 60 minutes tape can be cut into at least 30 clips, so there you have one clip per day. By doing multiple formats then you can make multiple updates in one day.
for example day 1: clip 1 in wmv at 12:00am, mp4 at 3am, dialup at 6am, and so on.
Hope this helps.