why pg doesn't need next example

output example

BEGIN
INSERT
ROLLBACK
BEGIN
INSERT
COMMIT
BEGIN
INSERT
COMMIT
BEGIN
INSERT
ROLLBACK
BEGIN
INSERT
COMMIT
0.430576
0.0382059
0.0331782

with_async.js

function insertRandomNumber(cb) {
	async.waterfall([
		function (cb) {
			console.log('BEGIN');
			client.query('BEGIN', cb);
		},
		function (result, cb) {
			console.log('INSERT');
			client.query('INSERT INTO foo VALUES (random()) RETURNING bar', cb);
		},
		function (result, cb) {
			if (result.rows[0].bar < 0.5) {
				console.log('COMMIT');
				client.query('COMMIT', cb);
			} else {
				console.log('ROLLBACK');
				client.query('ROLLBACK', cb);
			}
		}
	], cb);
}

async.waterfall([
	function (cb) { client.query('CREATE TEMP TABLE foo (bar real)', cb); },
	function (result, cb) {
		var i = 0;
		async.whilst(
			function () { return i < 5; },
			function (cb) { i++; insertRandomNumber(cb); },
			function (err) {
				client.query('SELECT bar FROM foo',
					function (err, results) {
						client.end();
						for (var i = 0; i < results.rowCount; i++)
							console.log(results.rows[i].bar);
						cb();
					}
				);
			}
		);
	}
]);

without_async.js

function insertRandomNumber(cb) {
	console.log('BEGIN');
	client.query('BEGIN', function () {
		console.log('INSERT');
		client.query('INSERT INTO foo VALUES (random()) RETURNING bar', function (err, result) {
			if (result.rows[0].bar < 0.5) {
				console.log('COMMIT');
				client.query('COMMIT', cb);
			} else {
				console.log('ROLLBACK');
				client.query('ROLLBACK', cb);
			}
		});
	});
}

client.query('CREATE TEMP TABLE foo (bar real)', function () {
	var i = 0;
	var doInserts = function () {
		insertRandomNumber(function () {
			i++;
			if (i < 5) {
				doInserts();
			} else {
				client.query('SELECT bar FROM foo', function (err, results) {
					client.end();
					for (var i = 0; i < results.rowCount; i++)
						console.log(results.rows[i].bar);
				});
			}
		});
	};
	doInserts();
});