Maybe its server is modified in some way to handle it or their software attaches all the pieces together.

I don't think it's software...How would you even pull that off? You would need to check for every variable name possible...

No you wouldn't. They're all easily accessible in the $_GET array.

foreach($_GET as $key => $value)

$_GET is an array? Why didn't anyone tell me?

But wait, how would I get each key to access the value? or is $key some sort of PHP constant there?

In foreach($_GET as $foo => $bar), $foo is assigned the key, and $bar is assigned that key's value.