Garbage collection and #%&$"%$

I’m driving crazy with this!
I don’t know why the guys from adobe make the things so complicated!!!
Why we can’t just delete an object when we don’t need it? how can we know if our object was deleted or not?
And even more, I will put an example, what’ happening in this case:

var mc:AnyClass: new AnyClass();
mc.addEventListener(...);
addChild(mc);
mc.removeEventListener(...);
removeChild(mc);
mc = new AnyClass();

I have created two instances of AnyClass but in the same var, so, I have two instances in memory or just one?

bye!!
enri.