Flash :: Convert From DisplayObject To Sprite With Loader?

Do you know why this AS3 code works:

var loader = new Loader();
loader.load(new URLRequest("http://127.0.0.1/items/boing.png")));
var o:DisplayObject = addChild(loader);
o.x = 100;
o.y = 100;

But if I cast to sprite it doesn't work? Ie the sprite appears on (0, 0) instead of (100, 100):

var loader = new Loader();
loader.load(new URLRequest("http://127.0.0.1/items/boing.png"))
var o:Sprite = Sprite(addChild(loader));
o.x = 100;
o.y = 100;

How would I properly have a sprite instead of a DisplayObject? I need some sprite's features (drag'n drop, useHandCursor...), yet I wish I could still use the very quick writing with the loader.