I'd say the point is that the idea that the legal system suddenly has no way to deal with witnesses claiming forgetfulness "because encryption" is absurd.

The only novel issues encryption brings to the table involve self incrimination, because, AFAIK, IANAL, etc., the only time an encryption key is inarguably protected by the fifth amendment is where the fact that the defendant knows the key is itself incriminating evidence, because the fifth amendment only applies to self-incriminating testimony, not other self-incriminating evidence in the defendant's possession (e.g., the contents of a hard drive, encrypted or not).