Meteor mongodb.connect vs MongoClient.connect

What is the difference between connecting mongodb.connect vs MongoClient.connect?

Sometimes I see this:

var mongodb = require( 'mongodb' ),
    express = require( 'express' ),
    node_acl = require( 'acl' ),
    port = 3500,
    app = express(),
    // The actual acl will reside here
mongodb.connect( 'mongodb://', _mongo_connected );

function _mongo_connected( error, db ) {

    if (error) throw error;

    var mongoBackend = new node_acl.mongodbBackend( db /*, {String} prefix */ );

    // Create a new access control list by providing the mongo backend
    //  Also inject a simple logger to provide meaningful output
    acl = new node_acl( mongoBackend, logger() );

    // Defining roles and routes

and then

//lets require/import the mongodb native drivers.
var mongodb = require('mongodb');

//We need to work with "MongoClient" interface in order to connect to a mongodb server.
var MongoClient = mongodb.MongoClient;

// Connection URL. This is where your mongodb server is running.
var url = 'mongodb://localhost:27017/my_database_name';

// Use connect method to connect to the Server
MongoClient.connect(url, function (err, db) {
  if (err) {
    console.log('Unable to connect to the mongoDB server. Error:', err);
  } else {
    //HURRAY!! We are connected. :)
    console.log('Connection established to', url);

    // do some work here with the database.

    //Close connection

Essentially correct connection is the same either way. So what is the difference?