Download Link Not Showing for Programmatically Added Downloadable Product in Order

I have been tasked for creating a order for a downloadable product and placing a order via Paypal and fortunately I've done the task pretty well.

But when the customer get his order email the download link for the product is not showing.

Below in my code that I've used :

<?php
if(!isset($_GET['p'])){
    $msg = '<h2>Wrong data passed!!</h2>';
}
else{
$product = Mage::getModel('catalog/product')->load($_GET['p']);
$cancel_url = Mage::getURL('').'paypal/standard/cancel/';
$return_url = Mage::getURL('').'paypal/standard/success/';
$notify_url = Mage::getURL('').'paypal/ipn/';

if(Mage::getStoreConfig('payment/paypal_standard/sandbox_flag')=='1'){
    $paypal_url = 'https://www.sandbox.paypal.com/cgi-bin/webscr?';
}
else{
    $paypal_url = 'https://www.paypal.com/cgi-bin/webscr?';
}
$price = number_format((float)$product->getPrice(),2,'.',''); 
$quote = Mage::getModel('sales/quote');

$quote->setCustomerEmail('magegurusit@gmail.com');

$quote->setStore(Mage::app()->getStore());   

$quoteItem = Mage::getModel('sales/quote_item')->setProduct($product);
$quoteItem->setQuote($quote);
$quoteItem->setQty(1);
$quote->addItem($quoteItem);

$addressData = array(
'firstname' => 'Guest',
'lastname' => 'Customer',
'street' => 'Some address on the earth',
'city' => 'Somewhere',
'postcode' => '123456',
'telephone' => '123456',
'country_id' => 'US',
'region_id' => 12, // id from directory_country_region table,
'use_for_shipping'=>1
);

$billingAddress = $quote->getBillingAddress()->addData($addressData);
/*$shippingAddress = $quote->getShippingAddress()->addData($addressData);
$shippingAddress->setCollectShippingRates(true)->collectShippingRates()
->setShippingMethod('flatrate_flatrate')
->setPaymentMethod('paypal_standard');*/

$quote->getPayment()->importData(array('method'=>'paypal_standard'));
$quote->collectTotals()->save();
$service = Mage::getModel('sales/service_quote', $quote);
try {
    $service->submitAll();
    $order = $service->getOrder();
    $invoice = $order->getIncrementId();
} catch (Exception $e){   
    Mage::log($e->getMessage());
}

Order is creating properly.
Don't know what little extra I'm missing in the above.
Please help me on this.
Thanks