Yes, I should of been more specific. I meant web server backend. Changed.

I agree. Modern languages are converging on ideas more than ever so it starts to become subjective. However, there exists a subtlety in feature focus. Compare concurrency and distributed programming in Erlang and Haskell, for example. If you're proficient in both and your domain demands high concurrency, why would you choose the lesser of the two which is Haskell?