Earlier quoted context omitted.
It doesn't work like that since certain videos use obfuscation methods that random cat videos don't.
I was under the impression that those obfuscation methods were exclusive to certain YouTube partners, including the RIAA members. If youtube-dl stopped supporting that method, it would still be a useful tool for the bulk of its use cases and the RIAA would no longer have any leg to stand on since it'd no longer be able to download their members' videos.
IMHO giving the client both the key and the algorithm to decode the content should not count as any form of protection, but the lawyers don't care...