Yes. JS runs everywhere that a modern browser runs and powers the web's client side.
Those are excellent reasons to use javascript to power your web applications client side as opposed to say Flash or ActiveX.
However, those have absolutely no bearing on writing your server code in JS.
The only reason to run JS on your server is so you can write the server side and client side in the same language. That's a debatable reason for running JS on your server.
Node incredible scalability around IO is also provided by a host of other not rushed and left to rot languages. Erlang, Go, C++, even Java has libraries for it.
When it comes to server side you can make a pretty good argument that the "emperor has no clothes".