Buying a DVD (especially used) is barely more expensive than renting, and there are all kinds of benefits to owning it, including the ability to watch it over a long period of time, lending it to friends, watching a really good movie multiple times or a second time with friends, etc. Plus you can buy any movie; you're not limited to the crappy mainstream selection of the video store/kiosk. Plus they have value (some of my films are worth more than when I purchased them) so that has to be factored in as well.

Note: I live in an area which doesn't have Netflix, so I'm comparing to renting from a store/kiosk.