Sure. Under Linux, processes and threads are both just tasks anyways. Processes may be nearly as efficient as threads, but you can do one better by not even having to spawn new threads per worker, which is what a concurrency model like Go's or Erlang's enable with ease. CGI and Websocketd also have significantly more costs than just a fork since they need to execute a target program.

And even forgetting the costs of forking, threads are not necessarily much better anyways. I can easily have a single Go program scheduling literally hundreds of thousands of Goroutines across just a few OS level threads and have no problems whatsoever, and in fact I've done exactly that in production, whereas I would never even dream of doing that with threads.

Node.JS's event loop model also doesn't need to spawn threads per connections.

When I say processes and forking are relatively expensive, I don't mean compared to doing the exact same thing with threads; I mean compared to more modern alternatives, like using an event loop or Goroutines.