The disruption is not about whether the paradigm is old or new. The fact is - today if you are building a small app and need some form of real-time features, your best bet is Node.js. Right from etherpad lite to socket.io you have the tools you need to be up and running and to support a few thousand concurrent users out of the box.
Of course, scaling it past that will be a problem with Node being single threaded and so on - but I believe that these are problems that Node.js will eventually address.
Sure - Tcl has had an event loop since sometime in the 90ies, and you could always do stuff in C.
However, Node is written from head to toe to take advantage of that style of coding, whereas Tcl never had the assumption that everything had to be async, so many calls block. Same thing with Python and Ruby, except that they're relative latecomers to the embedded
"select loop" game (sure, modern systems have moved on from select, but it still conveys the idea).
Erlang has been around for a while, and does async beautifully, but for every person who knows Erlang there are 10,000 who know Javascript.
At a very basic level, Node.js is a callback-based API that's based around some(probably select) notifier loop. That's not particularly new.