> A spec is a higher level of abstraction than code, which is a higher level of abstraction than machine code

No it’s not.

Just like a quick doodle is not an higher level representation of the Mona Lisa. Sure for someones that knows the latter, it can suggest it. Or for someone that doesn’t know it, it may provide some basis of conversation. But it’s not the real thing. You can’t provide a doodle of something and expect an artist that hasn’t seen it to paint it.

Doodling’s value is that it lets you iterate on ideas without the accidental constraints that comes with the implementation (choosing paints, finding references materials, deciding colors,…). Some necessary choices are kept for later, while you decide on the most important ones.

So a spec is useful in designing software, but it’s severely lacking in implementing it. And the decisions made in implementation are as important as the ones made in the design. Even more after a while in production.