Well perhaps, but to play Devil's advocate: this isn't a game.
There are two parts to DRM when combined with an anti-circumvention law. The first is the one that exists anyway: to attempt to make it as difficult as practically possible for someone to gain unrestricted access to the raw content. The other - which the DMCA (and its apparent German equivalent) adds - is to add legal liabilities for creating, possessing and/or using the tools, however easy, that break that encryption, should they ever come into being.
Us nerds have a tendency to misread laws and assume that rather than it being a reflection of the intent of the authors, that the language used is arbitrary and written by dolts to be interpreted in the widest possible context. Specifically we look at words like "effective" and rather than interpreting it in the context of the rest of the law, we go off on tangents and ask whether something is effective using other definitions within different contexts.
Is, for example, CSS effective? Well, I'd argue it is in context. It requires you use a specialized tool, designed specifically to break CSS, in order to access the content. It meets the definition in context. It doesn't meet the definition if you change the subject and say "Well, in 1998 it protected content, but does it now? Is it easy to find the tools needed to circumvent it?", but that's not the definition of effective that's implied by the context of the legislation - which is why better lawyers than us are not making that claim when protecting, say, Real Networks.
As for ROT-13.... well, maybe it is, maybe it isn't. My guess is it wouldn't, because ROT-13 doesn't require knowledge of any secrets beyond the fact it's being used to begin with, and the "tool" used to decrypt it is already built-in to a billion email, USENET, and so on clients. At the very least, if SuperdooperRayVD 4K discs in 2020 are encrypted using ROT-13, they'd have great difficulty persuading judges that millions of pre-existing USENET clients from the 1990s are illegal.