It is hard to quantify programmer productivity objectively, but most of us know subjectively when we are productive and when we are not and the difference that can make. If at my baseline I am 1x, at my peak productivity I can easily see myself being at 5-15x. (How this works and how to induce this boost is a separate discussion). I believe others experience what I am talking about. From here it isn't a far leap to think that another developer may just work at that pace naturally all the time.

I think this is the basis for the 10x developer mythos. Whether there is a great variation or Notch just recorded himself on days when he felt really productive (or the fact of recording himself made him productive) remains debatable.

Then again, I have seen my share of the 1/10x programmers, so it is possible that it is all relative. In either case, like you said, programming a computer is only a part of the job for most people. Gathering requirements, building a product, selling it, supporting it, marketing, all factor in. Otherwise, you might say that all a car mechanic ever does is change the oil.