[msherry]

My 2c is that R has a wealth of libraries and utilities (for statistics, machine learning, finance, etc.) that are not as easily available for other languages. Things like scikit-learn for Python close some of the gap, but looking at packages on http://cran.r-project.org/, it seems that Python might have some catching up to do.

I make no representation as to the quality of the libs available for R, as I don't have a whole lot of experience with it yet.

[epistasis]

Quality is all over the map in R, but given the choice between an R library and a Python library for the same recently developed stats method, I would think that the R library has been more widely used, had more attention from experts, and is probably more robust.