Why Same-Origin policy restricts access to Ajax but not to Php?

I'm working with this webservice it return an XML document.

When i call this webservice with Ajax i get:

XMLHttpRequest cannot load http://services.gisgraphy.com/geoloc/search?lat=36.81881&lng=10.16596&from=1&to=1. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://192.168.1.4:50000' is therefore not allowed access.

When do the same thing with PHP:

<?php
    $xml = simplexml_load_file('http://services.gisgraphy.com/geoloc/search?lat=50.209298&lng=10.245&from=1&to=1');
    print_r($xml);
?>

Print it without getting restricted.

I just wonder the difference between those cases, and why it work for php file only ?

Cheers.

Solution

When you run PHP code, you do it on your own server. Nothing should restrict you from accessing other website because it's your server.
When you run Javascript Code, you usually run it on a client web browser. You don't own the client machine. And the client machine want to protect itself from connecting to malicious website.

Imagine there's no same-origin policy :

$.ajax({
  url: "http://somedrugdealingwebsite.com"
})

Client's IP will be registered as visitor of drug dealing website.