> No. You can spin up multiple processes and handle the load with (for example) cluster[1].
Which is what I speculate they're doing, as they say they're running just four instances. Probably, they have servers capable of running 4 threads at the same time.
Yes (for now, we might take up V8 isolates).
> Would it not under-perform , say compared to Erlang or Netty, in a multi-core CPU.
No. You can spin up multiple processes and handle the load with (for example) cluster[1].
[1] http://learnboost.github.com/cluster/