I use R almost daily, and sure, for tasks involving math (& statistical analysis in particular) R is fantastic; however, to say "for hackers" (at least in my mind) would involve a less domain specific language -- like a scripting language (python or some such similar language) that has statistical analysis capabilities. Perhaps a matter of semantics, but in a similar vein, I imagine a book of the same title that used Octave would not be considered "for hackers" by most due to the specific/constrained functionality.

Just seems like "hacker" is such a buzz word now that it gets tacked onto a lot of stuff just to generate interest.