[Question] Why cant classes acces objects on stage?

Hi:)

Im trying to get used to packages and classes in AS3. Im used to put all code on the first frame of the timeline, but now i have 442 lines of code on the first frame. Yeah 442. And this is for a game engine so i thought i should put it inside some classes to make it easier to read an reusable. But i have noticed that if i create a class called Code and make a instance of that class like this:
[AS]var codeObject:Code = new Code();[/AS]
i get a bunch of errors because the class cant Acess the stage and the display list. Why??
i found a workaround by linking the class to a movieClip and and do this:
[AS]MovieClip(parent);[/AS]
But im just wondering why classes cant acess the stage:h: Anybody knows why??

Thanks:D