Its possible the parser was laid out to choke on octals as a way to protect the 'standard'. Its one decision to not support octals, and its another to make octal-style an error so those numbers are not parsed as base10.
Also, making a language X parser accept anything that is not in fact language X is nothing but a terrible idea. If there is one thing that standards are good for, it's interoperability. And if there is one thing that hurts interoperability, it's having different implementations of supposedly the same standard accept and reject different inputs. That's how you get websites that work in one browser, but not another, because one browser was so helpful to make up some meaning for your creative markup instead of rejecting it with an error message, which obviously helps you absolutely nothing with the next browser that is of a different opinion. If you think the spec is stupid, you have to change the spec, if you don't manage to do that, you still should implement the spec, because interoperability is more important than whether your program can read some input that isn't JSON and that therefore no other JSON parser is guaranteed to understand anyway.