Actually not everything in Node is non-blocking. IO is largely non-blocking by but there is also blocking IO in Node too (synchronous file system functions). Not to mention you definitely will block by doing something computationally intensive in a single tick of the reactor loop.

Have you ever written a non-trivial "real time" app in Ruby? I have (https://github.com/stevegraham/slanger). I think Ruby is actually very well suited to event driven apps. Eventmachine is a very mature library providing asynchronous I/O based on the same pattern as Node. Ruby also has fibers as a native language feature, allowing you to write asynchronous code that looks synchronous, i.e. no nested callback hell, and consequently this makes it a lot easier to write tests for.

Comparing Node to Rails is also absolute nonsense. Rails is a web framework and Node is much lower level than that. Rails is essentially a suite of DSLs for building web applications. Of course there are costs associated with that amount of abstraction.