How many concurrent requests can the six-line HTTP server on Node's front page serve? (I don't know the answer. I've taken a quick stab a few times on a few platforms, but I keep running into local TCP port exhaustion, leading to multi-second latency bubbles, long before I run into any Node.js or physical limit.)
Not sure if you changed the context from HTTP clients to HTTP servers intentionally, but it's true that the default of five connections is an outgoing connections restriction, not related to the HTTP server.
This client restriction is deeply irritating. A project I was involved with is about creating a general purpose hypermedia API, and building up documents involved following the links in parent documents back through the API, which meant that a single request can end up requiring hundreds of further calls to satisfy, which seemed like no problem at first with node.js' easy concurrency (and an auto-scaling fleet of EC2 servers), but the client connection limit turned out to be the cause of a lot of timeouts and prompted a lot of working around.
The client "limit" is just a tunable with a bad default value. You can tune this up and completely eliminate that limit. (The failure mode is pretty bad, but this comes from a lack of observability in abstraction design that pervades most code.) The server example, on the other hand, demonstrates the point that the default way to write a "hello world" web server actually scales very well.
