Think how simple it would be for Blockbuster to put something similar into effect
Think again. Blockbuster would lose 20% of their revenue base AND would demolish their ability to guarantee having titles on hand.
You obviously don't know much about the video rental business. If you want the true opinion, ask dcham (our resident expert on this board) just how hard your suggestion is for a brick/mortar store like Blockbuster.
Thinking that NFLX has a leg up on BBI because NFLX is a direct mail model instead of a retail store model, I think is a mistake. BBI can easily adopt a hybrid direct delivery model using its current distribution system.
Also, Blockbuster could institute a similar system of requiring you to return DVDs before being allowed to rent new ones, rather than imposing late fees. Obviously late fees would be imposed at some point to avoid people literally stealing DVDs. A plan with reasonable limits and exceptions could fairly easily be devised to still allow BBI to guarantee certain new releases are in stock.
In fact, BBI has already moved to longer term rentals on new releases so its customers should be experiencing much fewer incidences of incurring late fees or not having the time to watch the movies.