There are a few reasons that I still subscribe to the DVD service:
1. You can add a movie to the queue before it's in the theatre - This is nice because when I see a trailer for a movie I can generally add it to my queue right away. Several months later it shows up, sometimes I forgot about it and it's a neat surprise.
2. More selection - There are more movies available on DVD than streaming.
3. Less decision making - When my wife and I finally get a chance to sit down once a week and watch a movie without the kids we don't have to scroll through and decide on something, we just put in the DVD that we have for this week. There is a lot of evidence to show that reducing the number of decisions you need to make leads to less stress and the DVD queue makes that possible.