Rentals would be more appealing if the prices on the main services weren't so sky-high. Why is it that you can buy a 2-year-old AAA game (equivalent to a summer blockbuster) indefinitely for somewhere between $5-20 when it's on sale, but it costs at least $4 to rent an old movie for just a day in HD and sometimes more like $8? Instead of pricing taking digital into account movie studios keep trying to protect their DVD/bluray pricing.
In the end for a popular movie it's often a better experience to just pirate it. Netflix churns through movies so frequently that actually finding something that's not sub-Kangaroo Jack in quality takes longer than just torrenting.