There are a number of packages for relatively obscure statistical techniques (say, nonmetric multidimensional scaling) that are available for R, but not for python (that I have seen).
I also believe R is easier for statisticians who cannot and do not want to know how to program. There are many advanced techniques that are one-liners.
You've hit the nail on the head there. A programmer looks at R (or MATLAB) and says "this sucks as a programming language". An engineer or a scientist or a statistician says "so what, I'm not a programmer, nor do I want to be one, I've got actual work to do".
I also believe R is easier for statisticians who cannot and do not want to know how to program. There are many advanced techniques that are one-liners.