Mark Rahner at The Seattle Times asked his readers to tell him which movies or TV shows they most eagerly awaited to be released on DVD. "The Rockford Files" was the top vote-getter for TV shows, and King Kong is the most-wanted movie. He offers official explanations for why each is being delayed. See the rest of the list.
According to this article, "there are more than 44,000 titles on DVD as of this month", which means Netflix has 90% of them. One reason he gives for studios holding back titles is competition for store shelves; there isn't space for all the titles in release. I'd say studios should release more titles to Netflix, and not worry about the stores.