Regardless of whether or not 20TB is hording / excessive / inefficient, what it almost certainly is is replaceable. Let's face it, you aren't CERN, most of you data is probably media that you can reacquire with relative ease. It's not being stored because it's irreplaceable it's being stored because it's convenient. A RAID isn't too bad, but add in managing backups and where has that convenience gone? If it costs $10+/month to backup your ripped/downloaded movies, why not just sign up for Netflix?
Just make a list of all the replaceable data (e.g. videos you have the original disc for) you have and then buy an external hard disk / Blurays to back up the rest. If you lose your RAID, well, it'll be annoying to rebuild, but you built it once... (Besides, I doubt you could restore 20TB over residential internet less time!)
Some people have different use cases. A few years back I was visiting a friend in the boonies in Egypt and brought a TB of American movies and music along explicitly for her (she was putting me up for free while I was on a research project). With my 50Mbps connection and 250GB monthly cap, I could recreate the entire shebang in 4-5 months, but with her iffy ISP, she couldn't hope to download everything from me in her government's lifetime.
In the states we don't use petrol. We use gas.
Huh, I'm a United Statsian born and raised, and I've never used a duck to power my automobile.