From a newbie point of view, I would feel slightly cheated if uke fell without my doing the right thing to get them to fall. It breeds a false confidence in what you are doing and that can lead to all sorts of problems.
The attacks from my sempai come at a pace indicative of MY experience not theirs, and if I do things right they fall. If I don't they either don't go down straight away (giving me a chance to correct what is wrong) or they call a halt in order to let me know where I am going wrong so we can do it again.
I don't recall anyone yet who has gone over/down if I didn't do it right!!