I don't claim as extreme productivity differences as the parent but I've seen people do pretty impressive engineering feats and have heard first hand stories of

I don't claim as extreme productivity differences as the parent but I've seen people do pretty impressive engineering feats and have heard first hand stories of others. In the cases I've seen what makes people a lot more productive is experience. At Google, Ken and Russ ran circles around me in terms of writing compilers, but I had only written half a dozen toy compilers while someone like Ken has written many more production ones. My current co-worker Mikko just spent a few weeks re-writing the code to extract a mesh from our level set data. It's a distributed algorithm and our literature search didn't indicate it had ever been published. Starting with someone without domain experience it would be several weeks until the algorithm made sense. It probably would take years to replicate the feat. Programming is a very specialized endeavor. Some parts of more than others. My own experience indicates that individuals can have magnitudes of difference in their performance when applied to some of these specialized areas.