In the case of copyright you are not buying the media. You are buying a licensed right sent as media. If they wish to make no impediments to making a backup then maybe they have no fault.
Warranty is in no way predicated on issues of copyright or ability to backup. Warranty law applies to a copy of A Court of Thorns and Roses the same way it applies to a copy of Frankenstein.
Warranty is about fitness for use, merchantability, and honoring sales contracts. It has nothing to do with issues of intellectual property.
If you sold someone a book, filled with public domain content, and the ink faded after a week, you can't just throw up your hands and say that the buyer should have made another copy. You'd likely be liable for warranty of merchantability.
You are buying a DVD with the content on it. That's why it's $15 and not some sort of unlimited digital license that Netflex pays $millions for.
The fact that it's a limited license attached to the physical disc only makes my case more clear, I think. There's even less expectation that I have some claim to the content if the disc breaks in 20 years.
You are paying more for the DVD because copyright law and fair use apply to it including the right to backup. Companies prefer to sell you new online licensing as a scam.
The US didn't correctly defend the right to backup, but that leaves a funny grey zone where WB being bad at making DVDs means less ability to shame "piracy" tool makers because backups is normalized and in no way suspicious if the media isn't perfect like they said.
I don't understand why so many posters in this thread are being seemingly intentionally obtuse and insisting that the terms of of the original transaction are something entirely different from what it was. I expect better from this sites users than such naivety.
Copyright law has a long history ported from earlier media. People here want to say media is just some product but the US decided that is in no way true.
The nuance that most people miss is that prior to about the 1960s, books were effectively uncopyable on anything resembling scale. The only options would be to either copy it out in long hand in pen, or on a more industrial level to create new printing plates from scratch, resetting the entire thing character by character. You also wouldn't easily be able to replicate things like photographs or drawings.
It was only with the advent of toner based xerox in the 70s that photocopying books became vaguely practical, but still cost about 5 cents a page, at a time when a mass market paperback might cost $1.25.
Warranty is about fitness for use, merchantability, and honoring sales contracts. It has nothing to do with issues of intellectual property.
If you sold someone a book, filled with public domain content, and the ink faded after a week, you can't just throw up your hands and say that the buyer should have made another copy. You'd likely be liable for warranty of merchantability.