Distribution of software development skill in the entire population is probably normal. However, developers are not the entire population, they are a tiny slice of the right tail. So the distribution is more like an exponential distribution, which has the mean smaller than the median.
The performance of doctors follows the normal distribution. I think that extrapolating to programmers is not a huge stretch.
It used to be assumed that differences among hospitals
or doctors in a particular specialty were generally
insignificant. If you plotted a graph showing the
results of all the centers treating cystic fibrosis—or
any other disease, for that matter—people expected that
the curve would look something like a shark fin, with
most places clustered around the very best outcomes.
But the evidence has begun to indicate otherwise. What
you tend to find is a bell curve: a handful of team
with disturbingly poor outcomes for their patients, a
handful with remarkably good results, and a great
undistinguished middle.
The difference between doctors and programmers is that programmers get to build/leverage tools that are abstractions of other tools, hence you can have orders-of-magnitude differences in productivity between programmers
who use the best tools and those who don't. I assume that there's not that much variation between the way two different doctors carry out the same task like there is with programmers.
