No Saturday Mail Delivery Shouldn't Hurt Netflix, Gamefly In Long Run
Both services — Netflix for DVDs of movies and television shows, Gamefly for video games — rely on snail mail to get their goods into customers' hands. Other mail order businesses, such as Amazon or eBay don't rely solely on the post office for delivery and in most cases shipping costs fall to the customer, so if someone wants more expensive overnight delivery, they can pay for it.
One website went so far as to suggest that maybe Netflix should just buy the postal service and enact sweeping changes, saving money and keeping their Saturday service.

Netflix recently came to an agreement with Warner Brothers to wait 28 days before allowing subscribers to borrow the studio's new releases, this in hopes of getting more people to purchase the DVDs. In return, Warner allowed Netflix access to a much larger portion of its catalog for streaming. Netflix is only getting more videos in streaming mode, and this should accelerate as more customers demand it.
While the loss of Saturday delivery could hurt Netflix and Gamefly today, in the long run it might not make one whit of difference.