If you were to do this on Nginx you'd have to write the module in C.
You can't do it on Apache because of Apache's multi-process/thread model.
The fact that you can write a web server in a few lines of easy to understand and maintain Javascript that can handle over 10,000 concurrent connections without breaking a sweat is a breakthrough.
Node.js may do for server applications what Perl did for the Web in the 90's.