I always suspect the entertainment industry behind stuff like this. I know the only reason Netflix doesn't run on Linux(even though it runs on ChromeOS, which is linux) is because it is open source. With "secure boot", they could be sure there is no way for you to do anything with the video/audio stream except watch or listen. I think this is the real reason behind this madness. The compromise will be that your hardware will still run, but certain features will be missing without an "approved OS".
Some publishers of various kinds of media welcome the idea of treacherous computing for exactly the reason you suggest: If enough people agree to buy broken computers - so broken that they can not be programmed to copy certain files, for example - then big music companies, book companies, movie companies, etc. all have an easier time. They can, as you say, deliver content only on these broken devices, leading more people to give up their software freedom in exchange for more convenient access to TV or tunes.
It doesn't stop there, though. Some software vendors also like these restrictions. With treacherous computing, vendors can make themselves the exclusive providers of software and enjoy monopolistic pricing. In contrast, consider that the cost of a complete operating system for a non-broken computer starts with many decent options at a price of $0.
Treacherous computing also makes it easier for software vendors to monitor their users in ways that users can't control and might not even notice. There is no way, for example, to tell some devices not to "call home" and betray a users privacy to their vendors.
So it's a convergence of reasons, not just the "entertainment industry" (I guess you mean a few big companies, not everyone who sells entertainment) behind the thing.
