Node.js - core cluster module

Question

I am using the core cluster module in node v0.6.5. I have the following code:

var cluster = require('cluster');
var http = require('http');
var numWorkers = 3;

var count = 0;

if (cluster.isMaster) {
  for (var i = 0; i < numWorkers; i++) {
    cluster.fork();
  }
} else {
  console.log('createServer called');
  http.createServer(function (req, res) {
    count++;
    res.writeHead(200, {'Content-Type': 'text/plain'});
    res.end('Count is: ' + count.toString());
  }).listen(1337, "127.0.0.1");
}

Everytime I hit the page, the count is incremented twice, e.g. 1,3,5,7... Why does it increment twice?