Real Time Multiplayer in HTML5: only single-computer

I am having difficulty getting multiplayer games to be multi-computer, not just multi-browser tabs. I went through the Real Time Multiplayer in HTML5 tutorial (Build New Games, click here). It listens on port 4004, but I can't connect from my LAN's other computer by visiting 192.168.1.4:4004, even though I can connect with my Apache web server on port 80 by visiting 192.168.1.4 (I've since disabled Apache and forwarding port 80 on my router, instead I forward port 4004). I used to connect to Apache from the outside world by visiting my-domain.com (its DNS is hosted by my ISP). Now I can't connect from outside my LAN to my tutorial by visiting my-domain.com or my-domain.com:4004. The tutorial uses node.js, socket.io, and express. You start it by entering node app.js in a terminal. You add a new player by visiting 127.0.0.1:4004 or 192.168.1.4:4004. Here is the contents of app.js:

var
    gameport        = process.env.PORT || 4004,
    express         = require('express'),
    UUID            = require('node-uuid'),
    verbose         = false,
    app             = express()
  , http = require('http')
  , server = http.createServer(app)
  , io = require('socket.io').listen(server);

/* Express server set up. */

//The express server handles passing our content to the browser,
//As well as routing users where they need to go. This example is bare bones
//and will serve any file the user requests from the root of your web server (where you launch the script from)
//so keep this in mind - this is not a production script but a development teaching tool.

    //Tell the server to listen for incoming connections
server.listen( gameport );

    //Log something so we know that it succeeded.
console.log('\t :: Express :: Listening on port ' + gameport );

    //By default, we forward the / path to index.html automatically.
app.get( '/', function( req, res ){
    res.sendfile( __dirname + '/index.html' );
});
    //This handler will listen for requests on /*, any file from the root of our server.
    //See expressjs documentation for more info on routing.

app.get( '/*' , function( req, res, next ) {

        //This is the current file they have requested
    var file = req.params[0];

        //For debugging, we can track what files are requested.
    if(verbose) console.log('\t :: Express :: file requested : ' + file);

        //Send the requesting client the file.
    res.sendfile( __dirname + '/' + file );

});
/* Socket.IO server set up. */

//Express and socket.io can work together to serve the socket.io client files for you.
//This way, when the client requests '/socket.io/' files, socket.io determines what the client needs.

    //Create a socket.io instance using our express server
var sio = io;

    //Configure the socket.io connection settings.
    //See http://socket.io/
sio.configure(function (){

    sio.set('log level', 0);

    sio.set('authorization', function (handshakeData, callback) {
      callback(null, true); // error first callback style
    });

});
    //Enter the game server code. The game server handles
    //client connections looking for a game, creating games,
    //leaving games, joining games and ending games when they leave.
game_server = require('./game.server.js');

    //Socket.io will call this function when a client connects,
    //So we can send that client looking for a game to play,
    //as well as give that client a unique ID to use so we can
    //maintain the list if players.
sio.sockets.on('connection', function (client) {

        //Generate a new UUID, looks something like
        //5b2ca132-64bd-4513-99da-90e838ca47d1
        //and store this on their socket/connection
    client.userid = UUID();

        //tell the player they connected, giving them their id
    client.emit('onconnected', { id: client.userid } );

        //now we can find them a game to play with someone.
        //if no game exists with someone waiting, they create one and wait.
    game_server.findGame(client);

        //Useful to know when someone connects
    console.log('\t socket.io:: player ' + client.userid + ' connected');

        //Now we want to handle some of the messages that clients will send.
        //They send messages here, and we send them to the game_server to handle.
    client.on('message', function(m) {
        game_server.onMessage(client, m);
    }); //client.on message

        //When this client disconnects, we want to tell the game server
        //about that as well, so it can remove them from the game they are
        //in, and make sure the other player knows that they left and so on.
    client.on('disconnect', function () {

            //Useful to know when soomeone disconnects
        console.log('\t socket.io:: client disconnected ' + client.userid + ' ' + client.game_id);

            //If the client was in a game, set by game_server.findGame,
            //we can tell the game server to update that game state.
        if(client.game && client.game.id) {

            //player leaving a game should destroy that game
            game_server.endGame(client.game.id, client.userid);

        } //client.game_id

    }); //client.on disconnect

}); //sio.sockets.on connection

I realize that port forwarding and router issues may be outside the scope of most multiplayer game tutorials. Nevertheless, I hope someone can help me out here. Thanks.