I'm one of those who only keep Netflix because family watches it, i only watch one or two movies a month which is a very different from the dvd subscription days, back then it seemed like an endless stream of content that i'd never be able to get through, but the streaming service has never been as good as the dvd, i assume that's due to copyright or drm, something along those lines, but it's just a shame streaming has never matched the quality of the dvd sub.
I have a family member that still has the DVD plan. He will get a movie in, rip it out (Handbrake maybe?) and put it on a USB drive. His Roku is the Roku 2 (model 4210), which has a USB port. When he's done with the movie, he deletes it.
He has a streaming library of ripped Netflix movies that fluctuates up and down as he rips and watches them. I have made comments about his "pirate stash" but he actually does remove them from the USB drive when he's done. If he likes the move enough, he'll buy it from Amazon, VUDU, Google Play, Fandango Now, or some service that lets him access it, if it is (or when it becomes) available (often on sale). He's even had Netflix send him the same DVD 2 or 3 times in a year for movies he likes. His online library is huge. His ripped-DVD library is much smaller, but had he kept everything he ripped, it would be YUGE!
To your point, while there are some streaming content that's not available via DVD (mostly new stuff or Netflix originals), there is so much more DVD content that's not available via streaming. My family member has made the most of it. More work than most of us would want to do, but hey, whatever works, right?