It has to be open ended, otherwise you would not be able to make events that reference an object which may not exist yet.
If I were to make an event that said every x seconds sprite set y to self.y+1, as it is now it wouldn't do anything until one existed.
Error reporting really wouldn't add to ease of use in the long run, as you would have to have some silly event that asks, hey sprite do you exist?
But the kicker is you couldn't do that either because you want to make it so that you can't reference a nonexistent object.