My impression (and I am not a statistician/data scientist in my day job, so I would very much like to hear opposing perspectives) is that the R ecosystem is far more mature and widely adopted than scikit-learn for things like regression, classification, clustering etc.
The author also cites expensive MATLAB licenses as a driving force behind python adoption, but here too I'm skeptical. As a grad student, I get MATLAB for free. But I switched to R/pandas for data analysis because R has a native data structure for working with multidimensional datasets (i.e. data.frame).
To illustrate the utility of this, let's say you asked developers all over the US for their zipcode and salary and recorded the results in salary.poll.data. Here's an interesting question: what is the mean salary in each zipcode? In R, all sorts of libraries make this computation concise and highly readable. Using the excellent data.table package, you would do `salary.poll.data[, list(mean.salary.by.zip.code=mean(salary)), by=zipcode]`.
No such libraries exist in popular usage for MATLAB. You'd have to roll your own, or more likely, write a lot of crufty loops and conditional statements. (Or use higher order functions with map/reduce/filter, which, by the way, you would have to implement yourself).
For me at least, just having the right data structures for working with data makes R/pandas a clear winner for doing statistical analysis of data.