According to Moock's bible:
"Prior to ActionScript 3.0, the MovieClip class was used as an all-
purpose graphics container (Much like ActionScript 3.0 Sprite class is
used).
As of ActionScript 3.0, MovieClip is used onlymto control instances of
movie clip symbols created in the Flash authoring tool......"
MyShape in the first example is an instance of a MovieClip, and you
actually give it a name.
In other examples also you see
var clipContainer:Sprite = new Sprite(); which I think has the
function of what was a MovieClip before
Regards,
Karin