Google at least is known to use C/C++ for its backend. Python is (or was?) used in YouTube.
For data crunching, especially statistical jobs, Python is probably also a good fit although it's not as efficient but have a number of good statistical, mathematical and ai toolkits that seems to be more active.
For running more specialized jobs, R have even more tools, but is a bit more shaky as a general language although it is a nice functional language, as many tools are more scientists scaffolding rather than nice abstractions.
Then you have fortran and matlab. I've heard of using erlang as a fast real-time analytics tool too, but then you probably need to roll your own everything.
But what do you suggest? Node.js claim to fame is mainly that most web developers know it, and js have formed their mental image of what programing is and how a computer works.
Do people actually just skip that step and just directly deploy their R? That seems really scary.
The major difference I've seen between most of these companies is whether they've embraced Java 8 yet.
With the latest container-based toolchains I think it's not a bad idea to deploy some R-based services for certain type of tasks.
Google has quite a lot of java.
Java is huge in a lot of places.